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Diagnostic Circuit Check

NOTE: Perform diagnostic circuit check to diagnose CHECK ENGINE light function, ALDL connector and no-start condition.
  1. Compare data from vehicle being tested with SCAN TESTER DATA  table. This ensures self-diagnostic system is working properly. With ignition on and engine off, observe CHECK ENGINE light. If Code 12 is flashing, check for grounded diagnostic test circuit No. 451. See DIAGNOSTIC CHARTS, CHART A-2, for wiring schematic. If CHECK ENGINE light is off, See DIAGNOSTIC CHARTS, CHART A-1. If a steady CHECK ENGINE light is present, jump ALDL terminal "B" to terminal "A".
  2. The CHECK ENGINE light should flash a Code 12. If Code 12 is not present, See DIAGNOSTIC CHARTS, CHART A-2. If Code 12 is present, check if Scan tester displays ECM data. If no data is displayed, See DIAGNOSTIC CHARTS, CHART A-2.
  3. Start engine. If engine does not start, See DIAGNOSTIC CHARTS, CHART A-3. If engine starts, check for fault codes. If fault codes are present, see applicable chart under DIAGNOSTIC CODE CHARTS. Start with lowest code. If no fault codes are present, compare Scan tester data with typical data values. See SCAN TESTER DATA table. Values should be within typical ranges.
  4. If values are okay, see TESTS W/O CODES article in this section. If values are not within typical ranges, refer to the SYSTEM/COMPONENT TESTS article in this section.
SCAN TESTER DATA

Scan Position  Units Displayed  Typical Value 
Engine Speed RPM (2) 0-200 RPM
Desired Idle RPM (3) ECM Idle
Coolant Temp °C 85-105°
Map Volts (4) 1.0-2.0
Open/Closed Loop Open/Closed Loop (5) Closed Loop
TPS Volts .45-1.25
Throttle Angle 0-100% 0
Oxygen Sensor mV (6) 100-1000
Inj. Pulse Width Milliseconds .8-3.0
Spark Advance Degrees Varies
Fuel Integrator Counts 110-145
Block Learn Counts 118-138
Idle Air Control Counts/Steps 1-50
Park/Neutral PNRDL P or N
MPH & km/h 0-255 0
Torque Conv. Clutch On/Off Off
Battery Voltage Volts 13.5-14.5
Cooling Fan Relay On/Off (7) Off
A/C Request Yes/No No
A/C Clutch Shift Light (M/T) On/Off Off
(1) Test with engine at idle and in closed loop mode, upper radiator hose hot, throttle closed, transmission in Park or Neutral and all accessories off.
(2) From desired RPM (0-100 RPM in Drive).
(3) Varies with temperature.
(4) Depends on vacuum and barometric pressure.
(5) May enter open loop with extended idle.
(6) Varies continuously.
(7) Less than 216°F (102°C).
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