Diagnostic Circuit Check
NOTE:
The diagnostic circuit check, scan tool data table and diagnostic flow charts A-1, A-2 and A-3 should be used to diagnose the SERVICE ENGINE SOON light function, ALDL connector and no start condition.
- Compare data from vehicle being tested with SCAN TOOL DATA table. This ensures self-diagnostic system is working properly. With ignition on and engine off, check SERVICE ENGINE SOON light. If Code 12 is flashing, check for grounded diagnostic test circuit 451. See wiring diagram on CHART A-1. See Figure
. If no SERVICE ENGINE SOON light present, go to CHART A-1. See Figure
. If steady SERVICE ENGINE SOON light is present, jumper ALDL terminal "B" to "A".
- SERVICE ENGINE SOON light should flash a Code 12. If no Code 12 is present, go to CHART A-2. See Figure
. If a Code 12 is flashing, note if scan tool displays ECM data. If no data is displayed, go to CHART A-2. See Figure
.
- Start engine. If engine doesn't start, go to CHART A-3. See Figure
. If engine started, check for fault codes displayed. If fault codes present, see applicable code chart. Start with lowest code. If no fault codes present, compare scan tool data with typical data values. See SCAN TOOL DATA table in this article. Values should be within typical ranges.
- If values are okay, see TESTS W/O CODES
article. If values are not within typical ranges, see SYSTEMS & COMPONENT TESTING article.
SCAN TOOL DATA
| Scan Position |
Units Displayed |
Typical Value |
| Engine Speed |
RPM |
0-200 RPM |
| Desired Idle |
RPM |
ECM Idle |
| Coolant Temp |
°C |
85-105° |
| Manifold Air Temp |
°C |
10-80° |
| Map |
Volts |
1.0-2.0 |
| Open/Closed Loop |
Open/Closed Loop |
Closed Loop |
| TPS |
Volts |
.45-1.25 |
| Throttle Angle |
0-100% |
0 |
| Oxygen Sensor |
mV |
100-1000 |
| Inj. Pulse Width |
milliseconds |
.8-3.0 |
| Spark Advance |
# Of Degrees |
Varies |
| Fuel Integrator |
Counts |
Varies |
| Block Learn |
Counts |
118-138 |
| Idle Air Control |
Counts/Steps |
5-50 |
| Park/Neutral |
P/N & RDL |
P/N |
| VSS |
MPH or KM/H |
0 |
| Torque Conv. CL. |
On/Off |
Off |
| Battery Voltage |
Volts |
13.5-14.5 |
| Cool. Fan Relay |
On/Off |
Off (Below 226°F (108°C)) |
| A/C Request |
Yes/No |
No |
| A/C Clutch |
On/Off |
Off |
| Shift Light (M/T) |
On/Off |
Off |