Diagnostic Aids

Perform this test when instructed during QUICK TEST or if directed by other test procedures. This test is used to diagnose the following:

Faulty Fuel Pump Driver Module (FPDM)
Wiring Harness Circuits (B+, GND & VPWR To Fuel Pump Relay; FP, FPM, FP PWR, FP RTN & FPDM PWR).
Faulty Inertia Fuel Shutoff (IFS) Switch
Faulty Fuel Pump Relay
Faulty Powertrain Control Module (PCM)

NOTE: DTC P1233 and P1234 are identical, except DTC P1234 will not illuminate Malfunction Indicator Lamp (MIL).

1) DTC P1233 Or P1234: Check For KOEO DTCs P1233 Or P1234

These DTCs indicate PCM has stopped receiving duty cycle signal from Fuel Pump Driver Module (FPDM). Possible causes are:
- Inertia Fuel Shutoff (IFS) Switch Needs To Be Reset
- Open FPDM Ground Circuit
- Open Or Shorted FPM Circuit
- Faulty IFS Switch
- Faulty FPDM
- Faulty PCM
If DTC P1233 or P1234 is present in KOEO ON-DEMAND SELF-TEST, go to next step. If DTC P1233 or P1234 is not present in KOEO ON-DEMAND SELF-TEST, PCM is now receiving a signal from FPDM. Fault code may have been set due to Inertia Fuel Shutoff (IFS) switch being tripped, then reset. If engine starts, go to step 25). If engine is a no-start, disregard DTCs P1233 and P1234 at this time and repeat QUICK TEST . If any other DTCs are present, perform appropriate system test and repair as necessary. After repairing the engine no-start condition, go to step 25) to diagnose intermittent causes of DTC P1233 or P1234.

2) Check If Engine Starts

Attempt to start engine. If engine starts, go to step 15). If engine does not start, verify IFS switch is set (button depressed) and go to next step.

3) Check Power & Ground Circuits To FPDM

Turn ignition switch to OFF position. Disconnect FPDM connector. Turn ignition switch to ON position. Using a DVOM, measure voltage between FPDM harness connector FPDM PWR circuit terminal (VPWR circuit terminal on Continental) and ground circuit terminal. FPDM PWR or VPWR is the power circuit coming from the IFS switch to the FPDM. If voltage is more than 10.5 volts, replace FPDM. If voltage is 10.5 volts or less, go to next step.

4) Check Power To FPDM

Turn ignition switch to ON position. Using a DVOM, measure voltage between ground and FPDM harness connector FPDM PWR circuit terminal. If voltage is more than 10.5 volts, repair open ground circuit to FPDM. If voltage is 10.5 volts or less, go to next step.

Fig 1: Identifying ISO Micro Relay Cavity Terminals
Courtesy of FORD MOTOR CO.

9) Check For Ground To Fuel Pump Relay

Turn ignition switch to OFF position. Disconnect scan tool from DLC. Using a DVOM, measure resistance of ground circuit between fuel pump relay cavity No. 2 in battery junction box and negative battery terminal. See Fig 1. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in ground circuit.

10) Check For Open FPDM PWR Circuit

Using a DVOM, measure resistance of FPDM power circuit between fuel pump relay cavity No. 5 and FPDM harness connector terminal No. 9. See Fig 1 and Fig 2 . If resistance is less than 5 ohms, reconnect FPDM and go to next step. If resistance is 5 ohms or more, FPDM circuit circuit is open. Go to step 13) to isolate fault.

Fig 2: Identifying Fuel Pump Driver Module Connector Terminals
Courtesy of FORD MOTOR CO.

11) Check VPWR Circuit Voltage To Fuel Pump Relay

Turn ignition switch to ON position. Using a DVOM, measure VPWR circuit voltage between ground and fuel pump relay cavity No. 1. See Fig 1. If voltage is more than 10.5 volts, replace fuel pump relay. If voltage is 10.5 volts or less, repair open in VPWR circuit. See WIRING DIAGRAMS article.
NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 11) to step 13). No test procedures have been omitted.

13) Isolate Open In FPDM PWR Circuit

Disconnect Inertia Fuel Shutoff (IFS) switch connector. Measure resistance of FPDM PWR circuit between FPDM harness connector terminal No. 9 and IFS switch harness connector. See Fig 2. If both resistance measurements are less than 5 ohms, verify IFS switch is set (button depressed). If IFS switch is set, replace IFS switch. If either resistance measurement is 5 ohms or more, repair open in appropriate FPDM PWR circuit.
NOTE: PCM power relay is also referred to as EEC-V power relay.

14) Check For Open FPM Circuit

Turn ignition switch to OFF position. Disconnect FPDM connector. Disconnect PCM connector(s). Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Using a DVOM, measure resistance of FPM circuit between PCM harness connector terminal No. 40 and FPDM harness connector terminal No. 7. See Fig 2. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in FPM circuit.

15) Check FPM Circuit For Short To VPWR In Harness

Turn ignition switch to ON position. Using a DVOM, measure voltage between PCM harness connector terminal No. 40 and ground. If voltage is less than one volt, go to next step. If voltage is one volt or more, repair short to VPWR in FPM circuit.

16) Check FPM Circuit For Short To Ground In Harness

Turn ignition switch to OFF position. Disconnect scan tool from Data Link Connector (DLC). Using a DVOM, measure resistance between PCM harness connector terminal No. 40 and ground. If resistance is more than 10 k/ohms, go to next step. If resistance is 10 k/ohms or less, repair short to ground in FPM circuit.

NOTE: In the following test step, it is normal for voltage to cycle less than .02 volt and return to .02-1.0 volt.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 17) to step 25). No test procedures have been omitted.

17) Check For FPM Output From FPDM
Reconnect FPDM connector. Turn ignition switch to ON position. Using a DVOM, measure voltage between PCM harness connector terminals No. 40 and 51. If voltage is .2-1.0 volt, replace PCM. If voltage is not .2-1.0 volt, replace FPDM.

NOTE: With no fault detected, FPDM will send a 50 percent duty cycle signal on FPM circuit to PCM. FP M PID value should display 50 percent. Depending on scan tool being used, some scan tools will display a random value between 85-115 percent.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 25) to step 30). No test procedures have been omitted.

25) Check VPWR Circuit For Loss Of Power, & FPM Circuit To FPDM For Intermittent Short Or Open
Turn ignition switch to ON position. Using scan tool, select FP M PID from PID/DATA MONITOR & RECORD menu. Observe FP M PID value for indication of fault while performing the following. Fault will be indicated if FP M PID value changes from 50 percent, or value stops fluctuating:
- Wiggle and bend all FPDM system related circuits (FPDM PWR, GND or VPWR).
- Wiggle and bend FPM circuit between PCM and FPDM.
- Lightly tap on IFS switch, CCRM, FPDM and fuel pump relay to simulate road shock.
If any faults are found, isolate fault and repair as necessary. If no faults are found, problem cannot be duplicated at this time. Go to TEST Z, step 1).

NOTE: DTC P1235 and P1236 are identical, except DTC P1236 will not illuminate Malfunction Indicator Lamp (MIL). On LS models, FPDM functions are incorporated in Rear Electronics Module (REM). In the following steps, if directed to perform an FPDM action, complete the action using REM.

30) DTC P1235 Or P1236: Check For These DTC To Be Present In KOEO Or KOER On-Demand Self-Tests
These DTCs indicate that FPDM has detected an invalid or missing FP circuit signal from PCM. FPDM will send a message to PCM through FPM circuit, indicating failure has been detected. PCM will set the DTC when message has been received. Possible causes are:
- Open Or Shorted FP Circuit
- Faulty FPDM
- Faulty PCM
If DTC P1235 or P1236 is present in KOEO ON-DEMAND SELF-TEST or KOER ON-DEMAND SELF-TEST, DTC is a hard fault. Go to next step. If DTC P1235 or P1236 is not present in KOEO ON-DEMAND SELF-TEST or KOER ON-DEMAND SELF-TEST, fault is intermittent. Go to step 45).

31) Check For Open FP Circuit Between FPDM & PCM

Turn ignition switch to OFF position. Disconnect FPDM connector. Disconnect PCM connector(s). Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Using a DVOM, measure resistance of FP circuit between PCM harness connector and FPDM (REM on LS models) harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in FP circuit.

32) Check FP Circuit For Short To VPWR In Harness

Turn ignition switch to ON position. Using a DVOM, measure voltage of FP circuit between PCM harness connector and ground. If voltage is less than one volt, go to next step. If voltage is one volt or more, repair short to VPWR in FP circuit.

33) Check FP Circuit For Short To Ground In Harness

Turn ignition switch to OFF position. Disconnect scan tool from DLC. Using a DVOM, measure resistance of FP circuit between PCM harness connector and ground. If resistance is more than 10 k/ohms, go to next step. If resistance is 10 k/ohms or less, repair short to ground in FP circuit.

34) Check FP Circuit In FPDM

Reconnect FPDM. Turn ignition switch to ON position. Using a DVOM, measure voltage between PCM harness connector terminals No. 51 (PWR GND) and No. 80 (FP). If voltage is 4.5-5.5 volts, replace PCM. If voltage is not 4.5-5.5 volts, replace FPDM.
NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 34) to step 36). No test procedures have been omitted.

36) Check FPF PID

Turn ignition switch to ON position. Using scan tool, select FPF PID from PID/DATA MONITOR & RECORD menu. Observe FPF PID for 20 seconds. If FPF PID indicated YES during 20 second time period, go to step 40). If FPF PID indicates NO during whole 20 second time period, go to next step.

37) Check FP PID

Select FP PID from PID/DATA MONITOR & RECORD menu. If FP PID indicates 70-80 percent, go to next step. If FP PID does not indicate 70-80 percent, cycle ignition switch to OFF, then to ON position. Repeat step 36). If result is YES, go to step 40). If result is NO, replace PCM.

NOTE: PWM_DC1 PID indicates signal sent to REM from PCM on FP circuit.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 38) to step 40). No test procedures have been omitted.

38) Access REM PIDs & Check PWM_DC1 PID
Select PWM_DC1 PID from REM menu. If PWM_DC1 PID indicates 70-80 percent, turn ignition switch to OFF position. No fault is indicated, disregard DTC P1235 or P1236 at this time and diagnose problem by symptom. See SYMPTOMS in TROUBLE SHOOTING - NO CODES - EEC-V - CNG & GASOLINE article. If PWM_DC1 PID does not indicate 70-80 percent, replace REM.

40) Check REM Harness Voltage On FP Circuit At PCM

Turn ignition switch to OFF position. Disconnect PCM connector "A". Turn ignition switch to ON position. Using a DVOM, measure voltage between PCM harness connector terminal No. A58 and ground. If voltage is more than 8 volts, replace PCM. If voltage is 8 volts or less, replace REM.
NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 40) to step 42). No test procedures have been omitted.

NOTE: PWM_DC1 PID indicates signal sent to REM from PCM on FP circuit.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 42) to step 45). No test procedures have been omitted.

42) Check FP Circuit For Intermittent Problems
Turn ignition switch to ON position. Using scan tool, select PWM_DC1 PID from REM menu. Observe PWM_DC1 PID value for indication of fault while wiggling and bending FP circuit between REM and PCM. Fault will be indicated if PWM_DC1 PID value changes. If any faults are found, isolate fault and repair as necessary. If no faults are found, problem cannot be duplicated at this time. Go to TEST Z, step 1).

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 45) to step 47). No test procedures have been omitted.

45) Check FP Circuit For Intermittent Open Or Shorted Circuit
Turn ignition switch to ON position. Using scan tool, select FP M PID from PID/DATA MONITOR & RECORD menu. Observe FP M PID value for indication of fault while wiggling and bending FP circuit between FPDM and PCM. Lightly tap on FPDM to simulate road shock. Fault will be indicated if FP M PID value changes from 50 percent, or value stops fluctuating. If any faults are found, isolate fault and repair as necessary. If no faults are found, problem cannot be duplicated at this time. Go to TEST Z, step 1).

47) DTC P1237, P1238 Or P1641

These DTCs indicate FPDM has detected a fuel pump secondary circuit fault. This is due to an intermittent or hard fault. If DTC P1237, P1238 or P1641 is present in KOEO ON-DEMAND SELF-TEST or KOER ON-DEMAND SELF-TEST, DTC is a hard fault. Go to next step. If DTC P1237, P1238 or P1641 is not present in KOEO ON-DEMAND SELF-TEST or KOER ON-DEMAND SELF-TEST, fault is intermittent. Go to step 56).

48) Check If Engine Starts

Attempt to start engine. If engine starts, go to step 59). If engine does not start, go to next step to diagnose fuel pump secondary circuits.

49) Check FP PWR, FP RTN & Internal Fuel Pump Circuit Resistance

Turn ignition switch to OFF position. Disconnect scan tool from DLC. Disconnect FPDM connector. Using a DVOM, measure resistance between FPDM harness connector FP PWR circuit and FP RTN circuit terminals. If resistance is less than 10 ohms, go to next step. If resistance is 10 ohms or more, an open in secondary circuit exists. Go to step 54) to isolate fault.

50) Check FP RTN Circuit For Short To Power In Harness

Turn ignition switch to ON position. Using a DVOM, measure voltage of FP RTN circuit between FPDM harness connector and ground. If voltage is less than one volt, go to next step. If voltage is one volt or more, repair short to VPWR.

51) Check FP PWR Circuit For Short To Ground In Harness

Turn ignition switch to OFF position. Disconnect fuel pump connector. Using a DVOM, measure resistance of FP PWR circuit between FPDM harness connector and ground. If resistance is more than 10 k/ohms, go to next step. If resistance is 10 k/ohms or less, repair short to ground in FP PWR circuit.

NOTE: To perform step 52) without scan tool, fuel pump can be commanded on for one second by cycling ignition switch from OFF to ON position and repeating as necessary.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 52) to step 54). No test procedures have been omitted.

52) Check For VPWR To Fuel Pump
Reconnect FPDM and scan tool. Turn ignition switch to ON position. Connect DVOM between fuel pump harness connector FP PWR and FP RTN terminals. Using scan tool, access OUTPUT TEST MODE. See OUTPUT TEST MODE under ADDITIONAL SYSTEM FUNCTIONS. Command OUTPUTS ON. Fuel pump should turn on for about 5 seconds. With fuel pump commanded ON, if voltage is more than 10 volts, replace fuel pump. If voltage is 10 volts or less, verify battery is full charged. Ensure fuel pump command ON time did not time-out before voltage check was made. If battery is okay and command ON time did not time-out, replace FPDM.

54) Isolate Open Circuit

Turn ignition switch to OFF position. Disconnect fuel pump. Using a DVOM, measure resistance of FP PWR circuit and of FP RTN circuit between fuel pump harness connector and FPDM harness connector. Using a DVOM, measure internal resistance of fuel pump. If all resistance measurements are less than 10 ohms, no fault is detected at this time. Verify results of previous steps. If any resistance measurement is 10 ohms or more, repair open in FP PWR or FP RTN circuit, or replace fuel pump.
NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 54) to step 56). No test procedures have been omitted.

NOTE: When FPDM is detecting a secondary fuel pump circuit fault, a 75 percent duty cycle signal will be sent to PCM on FPM circuit. FP M PID value should display 75 percent. Depending on scan tool being used, some scan tools will display a random value between 250-400 percent.

56) Check For Intermittent DTC P1237, P1238 Or P1641
Turn ignition switch to ON position. Using scan tool, select FP M PID from PID/DATA MONITOR & RECORD menu. If FP M PID value is 75 percent or is varying between 250-400 percent, a hard fault is present, go to step 48). If FP M PID value is not 75 percent or varies within a range of 250-400 percent, DTC P1237, P1238 or P1641 is intermittent, go to next step.

57) Check Fuel Pump Secondary Circuits For Intermittent Open Or Short
Turn ignition switch to ON position. Using scan tool, select FP M PID from PID/DATA MONITOR & RECORD menu. Observe FP M PID value for indication of fault while wiggling and bending FP PWR and FP RTN circuits between FPDM and fuel pump. Lightly tap on FPDM to simulate road shock. Fault will be indicated if FP M PID value changes from 50 percent, or varies within a range of 85-115 percent. If any faults are found, isolate fault and repair as necessary. If no faults are found, go to next step.

58) Check FP PWR Circuit For Short To Ground

Turn ignition switch to OFF position. Disconnect FPDM. Connect a test light between FPDM harness connector FP PWR circuit and FPDM PWR circuit terminals. Turn ignition switch to ON position. Observe test light for indication of fault while wiggling and bending FP PWR circuit between FPDM and fuel pump. If a fault is indicated, test light will turn on (indicating short to ground). If any faults are found, isolate fault and repair as necessary. If no faults are found, problem cannot be identified at this time. Turn ignition switch to OFF position, reconnect FPDM and go to TEST Z, step 1).

59) Check FP PWR Circuit For Short To VPWR

Turn ignition switch to OFF position. Disconnect FPDM connector. Turn ignition switch to ON position. Using a DVOM, measure voltage of FP PWR circuit between ground and FPDM harness connector. If voltage is less than one volt, go to next step. If voltage is one volt or more, repair short to VPWR in FP PWR circuit.

60) Check FP RTN Circuit For Short To Ground

Ensure ignition switch is turned to ON position. Using a DVOM, measure voltage between FPDM harness connector FPDM PWR circuit and FP RTN circuit terminals. If voltage is less than one volt, replace FPDM. If voltage is one volt or more, repair short to ground in FP RTN circuit.
NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 60) to step 62). No test procedures have been omitted.

62) Check REM/FP PWR Circuit Voltage To REM

Ensure ignition switch is turned to ON position. Using a DVOM, measure voltage between ground and REM harness connector J1 terminal No. 1 (FP PWR). If voltage is more than 10.5 volts, repair open ground circuit from REM harness connector J1 terminal No. 2. If voltage is 10.5 volts or less, go to next step.

63) Check For B+ Voltage To Fuel Pump Relay

Turn ignition switch to OFF position. Remove fuel pump relay from battery junction box in engine compartment. Using a DVOM, measure voltage between ground and fuel pump relay cavity No. 3. See Fig 1. If voltage is more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, check for blown fuse No. 417 (15-amp) located in battery junction box. If fuse is blown, check for short to ground in B+ circuit or short to voltage in FP RTN circuit before replacing fuse. If fuse is okay, repair open in Red/Blue wire between fuse No. 417 and fuel pump relay cavity No. 3.

64) Check For IGN START/RUN Voltage (Through IFS Switch) To Fuel Pump Relay

Turn ignition switch to OFF position. Disconnect REM connector J3. Turn ignition switch to ON position. Using a DVOM, measure voltage of IGN START/RUN circuit between ground and REM harness connector J3 terminal No. 8 (Green/White wire). If voltage is more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, check for blown fuse No. 204 (5-amp) in central junction box located behind right kick panel. If fuse is blown, check for short to ground in IGN START/RUN circuit before replacing fuse. If fuse is okay, go to step 69) to isolate open circuit.

65) Check Ground Circuit To Fuel Pump Relay

Turn ignition switch to OFF position. Using a DVOM, measure resistance of ground circuit between fuel pump relay cavity No. 1 and ground. See Fig 1. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in ground circuit.

66) Check REM/FP PWR Circuit Continuity

Using a DVOM, measure resistance of REM/FP PWR circuit between fuel pump relay cavity No. 5 and REM harness connector terminal No. 1. See Fig 1. If resistance is less than 5 ohms, replace fuel pump relay. If resistance is 5 ohms or more, repair open in REM/FP PWR circuit.

67) Check REM/FP PWR, REM GND & Related Fuel Pump Relay Circuits For Intermittents

Turn ignition switch to OFF position. Disconnect REM connector J1 if not previously disconnected. Connect test light between REM connector J1 terminals No. 1 (REM/FP PWR) and No. 2 (GND). Turn ignition switch to ON position. Observe test light for indication of fault while wiggling and bending REM/FP PWR circuit and GND circuits to REM. Shake, wiggle and bend GND, IGN START/RUN and B+ circuits to fuel pump relay. Lightly tap on fuel pump relay and IFS switch to simulate road shock. If a fault is indicated, test light will turn off. If any faults are found, isolate fault and repair as necessary. If no faults are found, go to next step.

68) Check FP PWR & FP RTN Circuits For Intermittent Problems

Turn ignition switch to OFF position. Using a DVOM, measure resistance between REM connector J1 terminals No. 11 (FP PWR) and No. 12 (FP RTN). Observe DVOM for indication of fault while wiggling and bending FP PWR and FP RTN circuits between REM and fuel pump. Perform same procedure with DVOM connected between REM connector J1 terminal No. 12 (FP RTN) and ground. A fault is indicated when resistance changes suddenly. If any faults are found, isolate fault and repair as necessary. If no faults are found, problem cannot be identified at this time. Turn ignition switch to OFF position. Remove DVOM, reconnect REM and go to TEST Z, step 1).

69) Locating Open in IGN START/RUN Circuit

Disconnect IFS switch. Using a DVOM, measure resistance between IFS switch terminals. Record resistance reading. Also, measure resistance of IGN START/RUN circuit between fuel pump relay cavity No. 2 and IFS. If both resistance measurements are less than 5 ohms, repair open in IGN START/RUN circuit between fuse No. 204 (5-amp) in central junction box and IFS switch. If resistance is 5 ohms or more in either measurement, replace IFS switch or repair open in IGN START/RUN circuit between fuel pump relay cavity No. 2 and IFS. Ensure fuel pump motor diode is okay. See WIRING DIAGRAMS article.

NOTE: Diagnostic steps 70)- 72) are performed when directed here from TEST HC, step 2).

70) Check Battery Voltage With Outputs Commanded On
Turn ignition switch to OFF position. Disconnect fuel pump connector. Connect scan tool to DLC. Turn ignition switch to ON position. Connect a DVOM between battery terminals. Using scan tool, access OUTPUT TEST MODE. See OUTPUT TEST MODE under ADDITIONAL SYSTEM FUNCTIONS. While monitoring battery voltage, command OUTPUTS ON. Record voltage measurement within 5 seconds. If battery voltage is more than 11 volts, command OUTPUTS OFF and go to next step. If battery voltage is 11 volts or less, battery voltage is low. Service battery/charging system as necessary. See appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS.

71) Check Ground Circuit To Fuel Pump

Turn ignition switch to OFF position. Connect DVOM between fuel pump harness connector FP PWR circuit terminal and negative battery terminal. Turn ignition switch to ON position. Using scan tool, command OUTPUTS ON. Record voltage measurement within 5 seconds. If voltage is 10.5 volts or less, ground circuit to fuel pump is okay. Go to next step. If voltage is more than 10.5 volts, locate and repair high resistance in ground circuit to fuel pump. Check all wiring and connectors for fuel pump and FPDM (REM on LS) for corrosion or damage. Check FPDM (REM on LS) ground connection to chassis ground. Repair as necessary.

72) Check Voltage To FPDM

Turn ignition switch to OFF position. Disconnect FPDM connector. Turn ignition switch to ON position. Using a DVOM, measure voltage of FPDM PWR circuit between negative battery terminal and FPDM harness connector. If voltage is more than 10.5 volts, go to next step. If voltage is 10.5 volts, or less, insufficient voltage is being supplied to FPDM.
NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 72) to step 80). No test procedures have been omitted.

80) Check FP RTN Circuit For Short To Ground

Turn ignition switch to OFF position. Disconnect REM connector J1. Turn ignition switch to ON position. Using a DVOM, measure voltage between REM harness connector J1 terminals No. 1 (REM/FP PWR) and No. 12 (FP RTN). If voltage is less than one volt, go to step 67). If voltage is one volt or more, repair short to ground in FP RTN circuit.
NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 80) to step 85). No test procedures have been omitted.

NOTE: Diagnostic steps 85)- 86) are performed when directed here from SYMPTOMS in TROUBLE SHOOTING - NO CODES article.

85) Perform REM Self-Test To Verify IFS Switch Input To REM
Using scan tool, perform Self-Test on Rear Electronics Module (REM). If DTC B2172 is present, go to next step. If DTC B2172 is not present, go to TEST A, step 1).

86) B2172: Check IFS Switch Input Circuit To REM

Turn ignition switch to OFF position. Disconnect REM connector J3. Turn ignition switch to ON position. Using a DVOM, measure voltage of IFS INPUT circuit between ground and REM harness connector J3 terminal No. 8. If voltage is 10.5 volts or less, turn ignition switch to OFF position and ensure IFS switch is not open. If IFS switch is okay, repair open circuit between IFS switch and REM harness connector. If voltage is more than 10.5 volts, perform the following:
- If engine is a no-start and REM DTC B2172 was received in On-Demand Self-Test mode, replace REM.
- If engine will start or REM DTC B2172 is a Continuous Memory DTC, DTC is intermittent. If engine is a no-start, return to SYMPTOMS in TROUBLE SHOOTING - NO CODES article to continue diagnosis. If engine will start, go to TEST Z, step 1).