DIAGNOSTIC CIRCUIT CHECK
The diagnostic circuit check is an organized approach for identifying a problem caused by the Fuel Injection System. Driver complaints fall into 3 categories: Steady "SERVICE ENGINE SOON" light, driveability problems, and engine "CRANKS BUT WON'T RUN."
- A steady "SERVICE ENGINE SOON" light, with ignition "ON" and engine stopped, confirms battery and ignition voltage to the ECM.
- Code 12 should flash 3 times, followed by any other trouble codes stored in memory.
- Record all stored codes except Code 12.
- With the engine running and the diagnostic terminal grounded, the ECM will respond to the O2 sensor signal voltage and use the "SERVICE ENGINE SOON" light to display this information as follows: 4A) Closed loop confirms that O2 sensor voltage is being used to control fuel delivery. Signal voltage will vary from .35-.55 volt. 4B) Open loop confirms that O2 sensor voltage is unusable to the ECM. Signal voltage is a fixed value between .35-.55 volt. System will flash open loop for 30 seconds to 2 minutes or until O2 sensor reaches operating temperature. 4C) O2 sensor signal voltage will be less than .35 volt. 4D) O2 sensor signal voltage will be more than .55 volt.
- Road test of the system in the field service mode must be done at steady speeds. In this mode the following conditions may be observed and considered normal: Light "ON" too long under acceleration, light "OFF" too long under deceleration, light on too long at idle with idle below 1200 RPM.
Diagnostic Circuit Check (All Engines). Scheme 33
Chart A1 - No "CHECK ENGINE" Light (2.0L). Scheme 34
Chart A2 - No Code 12, "CHECK ENGINE" Light ON Steady (2.0L). Scheme 35
Chart A3 (1 of 2) - Engine Cranks, But Will Not Run (2.0L). Scheme 36
Chart A4 2 of 2) - Engine Cranks, But Will Not Run (2.0L). Scheme 37
Chart A5 (1 of 3), Fuel System Diagnosis (2.0L). Scheme 38
Chart A6 (2 of 3), Fuel System Diagnosis (2.0L). Scheme 39
Chart A7 (3 of 3), Fuel System Diagnosis. Scheme 40
Code 13 - Open Oxygen Sensor Circuit (2.0L). Scheme 41
Code 14 - Coolant Sensor Circuit Voltage Too Low (2.0L). Scheme 42
Code 15 - Coolant Sensor Circuit Voltage Too High (2.0L). Scheme 43
Code 21 - Throttle Position Sensor (TPS) Voltage High (2.0L). Scheme 44
Code 21 - Throttle Position Sensor (TPS) Voltage Low (2.0L). Scheme 45
CODE 24 - VEHICLE SPEED SENSOR (VSS) BUFFER ATTACHED TO I.P.
CLUSTER
Code 24 - VSS Buffer Attached to I.P. Cluster (2.0L). Scheme 46
Code 33 - MAP Sensor Voltage Too High (2.0L). Scheme 47
Code 34 - MAP Sensor Voltage Too Low (2.0L). Scheme 48
Code 42 - Electronic Spark Timing (EST) (2.0L). Scheme 49
Code 44 - Lean Exhaust Indication (2.0L). Scheme 50
Code 45 - Rich Exhaust Indication (2.0L). Scheme 51
CODE 51, PROM FAILURE
Check that all pins are fully inserted in the socket. If okay, clear memory and recheck. If CODE 51 resets, replace ECM.
CODE 52 FUEL CALPAC MISSING
If Code 52 appears, Fuel Calpac is missing.
CODE 55, REPLACE ECM
If Code 55 appears, ECM needs to be replaced.
CHART C1 - ECM REPLACEMENT CHECK CHART
In order to reduce incidents of repeat ECM failure, a revised ECM diagnostic procedure is available. Beginning in 1982, most ECMs are equipped with Integrated Circuits (IC) in place of separate transistors to operate various controlled components.
These ICs, called Quad-Drivers (QDR), have 4 separate outputs, meaning that each QDR can operate up to 4 different components. An inoperative QDR can result in ECM output becoming open or shorted to ground. Often, all 4 outputs of a QDR will fail, even if just one QDR circuit is faulty.
Refer to the following tables to determine which ECMs contain QDRs. Since this procedure is not applicable to ECMs which do not contain QDRs, those ECMs are not listed.
Performing the diagnostic flow chart will identify an inoperative QDR. Once the circuit is identified, it must be repaired to eliminate repeat ECM failure. This diagnostic procedure must be used when "Replace ECM" is the conclusion of any procedure.
| Application | (1) Output Terminals | |
|---|---|---|
| 1226458, 1226460 | ||
| QDR No. 1 | C1, C2, A2, A3 | |
| QDR No. 2 | A4, A5, A7, A7 | |
| 1225610, 1226100, 1226026, 1226430 | ||
| QDR No. 1 | Black 9, Black 14, Black 16, White 20 | |
| QDR No. 2 | Black 7, Black 22, White 19, White 19 | |
| 1226026, 1226430 | ||
| QDR No. 1 | Black 9, Black 14, Black 16, White 20 | |
| QDR No. 2 | Black 7, Black 22, White 19, White 19 | |
| 1226156 | ||
| QDR No. 1 | White 20, Black 7, Black 9 | |
| 1226864 | ||
| QDR No. 1 | Black 7, Black 9, White 20 | |
| 1226867 | ||
| QDR No. 1 | A2, A3, A4, C2 | |
| QDR No. 2 | C1, A5, A7, A7 | |
| 1226868, 1227746, 1227747 | ||
| QDR No. 1 | A2, A3, C1, C2 | |
| QDR No. 2 | A4, A5, A7, A7 | |
| 1227137, 1227429 | ||
| QDR No. 1 | A2, A3, C1, C2 | |
| QDR No. 2 | A4, A5, A7, A7 | |
| 1227748 | ||
| QDR No. 1 | Black 7, Black 7, Black 18, White 18 | |
| QDR No. 2 | Black 3, Black 4, White 21, White 22 | |
| 1227749 | ||
| QDR No. 1 | E7, E8, E9, F7 | |
| QDR No. 2 | F1, F2, F3, F4 | |
| 1226028, 1226462, 1226930 | ||
| QDR No. 1 | Blue 9, Blue 14, Blue 16, Red 20 | |
| QDR No. 2 | Blue 7, Blue 22, Red 19, Red 19 | |
| (1) Colors refer to ECM connector colors. | ||
| (1) | Colors refer to ECM connector colors. |
ECM QDR IDENTIFICATION
