- Flow of Diagnosis - Start Here

Flow Of Diagnosis:

NOTE:

A. Since this is the starting point for all diagnostic procedures or finding the cause of an emissions test failure, always begin here and always follow the flow chart as directed.
B. For trouble code diagnosis and Charts A-1 and A-2, refer to COMPUTERIZED ENGINE CONTROLS/DIAGNOSIS AND TESTING.

1. Get an accurate description of the complaint and verify. Include filling out the DRIVEABILITY WORKSHEET and VEHICLE REPAIR HISTORY. Refer to INFO TYPE/TECHNICAL MANAGEMENT SUPPORT for forms.

Perform Underhood Inspection:

a. Check vacuum hoses for splits, kinks, and proper routing.
b. Check ignition wires for cracking, hardness, and proper connections at both the distributor and spark plugs.
c. Check all wiring for proper connections, pinches, and cuts.
d. Check wiring harness for proper routing.
e. Check for missing components.

2. Check TSBs for manual updates, testing procedures, warranty and recall information.

3. Check for latest PROM updates and replacements. Refer to COMPUTERIZED ENGINE CONTROLS/PROM I.D.

4. To obtain stored trouble codes from the ECM, it is necessary to jumper the BLACK wire and the BLUE/YELLOW wire at the ECM check connector, located under the hood by the battery.

5. A Code 12 is normal, and is used to verify that the diagnostic circuit is functioning properly.

NOTE: Code 12 will NOT flash three (3) times, but all other codes will.

6. If the problem is "Engine Cranks, But Will Not Run," refer to DIAGNOSTIC CHARTS/ENGINE CRANKS BUT WILL NOT RUN (A-3).

7. At this point it would be advantageous to know if the problem is fuel related or other. Choose the path that best suits the individual situation.

a. For fuel related problems, refer to Powertrain Management/Computers and Control Systems/Testing and Inspection/Procedures/Diagnosis by Symptom.
b. For all other systems, refer to COMPUTERIZED ENGINE CONTROL/DIAGNOSIS AND TESTING PROCEDURES/TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM.

DIAGNOSTIC CIRCUIT DEFINITIONS:

Code 12-ECM diagnostics are functional.
Code 13-Oxygen Sensor circuit - open
Code 14-Coolant Temperature Sensor (CTS) circuit - low temp. indicated
Code 15-Coolant Temperature Sensor (CTS) circuit - high temp. indicated
Code 21-Throttle Position Sensor (TPS) circuit - signal voltage high
Code 22-Throttle Position Sensor (TPS) circuit - signal voltage low
Code 23-Intake Air Temperature Sensor (IAT) circuit - low temp. indicated
Code 24-Vehicle Speed Sensor (VSS)
Code 25-Intake Air Temperature Sensor (IAT) circuit - high temp. indicated
Code 31-Manifold Absolute Pressure Sensor (MAP) circuit - signal voltage high, low vacuum
Code 32-Manifold Absolute Pressure Sensor (MAP) circuit - signal voltage low, high vacuum
Code 41-Ignition Signal circuit - no signal
Code 42-Fifth Gear Switch circuit grounded - M/T only
Code 42-Torque Converter Clutch (TCC) lock-up signal circuit - signal voltage remains on at all times - A/T only
Code 44-Idle Switch circuit - open or improper adjustment
Code 45-Idle Switch circuit - grounded or improper adjustment
Code 51-EGR System & Re-circulated Exhaust Gas Temperature Sensor (REGTS) - temp. to low or high
Code 53-Ground circuit (California Only) - open