SERVICE MANUAL REVISION 6E3-A DRIVEABILITY & EMISSIONS
Model and Year: 1988 CORSICA/BERETTA SERVICE MANUAL SUPPLEMENT
The following pages, 6E3-A-49 through 52 of the 1988 Corsica/Beretta Service Manual Supplement should be affixed over the pages currently in your manual. The replacement pages include expanded diagnostics.
CODE 43 ELECTRONIC SPARK CONTROL (ESC) CIRCUIT 2.8L (VIN W) "L" SERIES (PORT)
Circuit Description:
The knock sensor is used to detect engine detonation and the ECM will retard the electronic spark timing based on the signal being received. The circuitry within the knock sensor causes the ECM 5 volts to be pulled down so that under a no knock condition, CKT 496 would measure about 2.5 volts. The knock sensor produces an A/C signal which rides on the 2.5 volts DC voltage. The amplitude and signal frequency is dependent upon the knock level. If CKT 496 becomes open or shorted to ground, the voltage will either go above 3.5 volts or below 1.5 volts. If either of these conditions are met for about 1/2second, a Code 43 will be stored.
Test Description: Numbers below refer to circled numbers on the diagnostic chart (See Figure 2 & 3).
1. This step determines if conditions for Code 43 still exist (voltage on CKT 496 above 3.5 volts or below 1.5 volts). The system is designed to retard the spark 6 DEG., if either condition exists.
2. The ECM has a 5 volt pull-up resistor, which applies 5 volts to CKT 496. The five volt signal should be present at the knock sensor terminal during these test conditions.
3. This step determines if the knock sensor resistance is 3900 ohms +/- 15%. If the resistance is between 3300 to 4500 ohms, the sensor is OK.
4. If CKT 496 is not open or shorted to ground and the voltage reading is below 4 volts, the most likely cause is an open circuit in the ECM. It is possible that a faulty Mem-Cal could be drawing the 5 volt signal down and it should be replaced, if a replacement ECM did not correct the problem.
Diagnostic Aids:
Check CKT 496 for a potential open or short to ground. Also, check for proper installation of Mem-Cal. Refer to "Intermittents" in Section "B".
CODE 44 OXYGEN SENSOR CIRCUIT (LEAN EXHAUST INDICATED) 2.8L (VIN W) "L" SERIES (PORT)
Circuit Description:
The ECM supplies a voltage of about .45 volts between terminals "E14" and "E15." (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volts.) The 02 sensor varies the voltage within a range of about 1 volt if the exhaust is rich, down through about .10 volts if exhaust is lean. The sensor is like an open circuit and produces no voltage when it is below about 315 DEG. C (600 DEG. F). An open sensor circuit or co Id sensor causes "Open Loop" operation.
Test Description: Numbers below refer to circled numbers on the diagnostic chart (See Figure 4).
1. Code 44 is set when the 02 sensor signal voltage on CKT 412 - Remains below .2 volts for 6O seconds or more - And the system is operating in "Closed Loop."
Diagnostic Aids:
Using the "Scan," observe the block learn values at different rpm and air flow conditions. The "Scan" also displays the block cells, so the block learn values can be checked in each of the cells to determine when the Code 44 may have been set. If the conditions for Code 44 exist, the block learn values will be around 150.
- O 2 Sensor Wire. Sensor pigtail may be mispositioned and contacting the exhaust manifold.
- Check for intermittent ground in wire between connector and sensor.
- MAF Sensor. A mass air flow (MAF) sensor output that causes the ECM to sense a lower than normal air flow will cause the system to go lean. Disconnect the MAF sensor and if the lean condition is gone, check for a Code 33 or 34.
- Lean Injector(s). Perform injector balance test CHART C-2A.
- Fuel Contamination. Water, even in small amounts near the in-tank fuel pump inlet can be delivered to the injectors. The water causes exhaust and can set a Code 44.
- Fuel Pressure. System will be lean if pressure is too low. It may be necessary to monitor fuel pressure while driving the car at various road speeds and/or loads to confirm. See Fuel System diagnosis CHART A-7.
- Exhaust Leaks. If there is an exhaust leak, the engine can cause outside air to be pulled into the exhaust and past the sensor. Vacuum or crankcase leaks can cause a lean condition.
- If the above are OK, it is a faulty oxygen sensor.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.
