SER. MAN. UPDATE SEC. 6E1 REVISED CODE 44/45

Subject: REVISED CODE 44/45

Model and Year: 1987-88 CAPRICE AND CAMARO WITH 5.OL AND 5.7L ENGINES

TO: ALL CHEVROLET DEALERS

The information in this bulletin replaces the Code 44 (Lean Exhaust) and Code 45 (Rich Exhaust) Diagnostic Charts and Facing Pages found in DRIVEABILITY AND EMISSIONS (SECTION 6E1) of the 1987-1988 5.OL (VIN G/H) and 5.7L (VIN 6) "B" and "F" Carline Service Manuals.

CODE 44 LEAN EXHAUST INDICATION CARBURETED

Circuit Description:

Code 44 indicates that the ECM has seen 02 sensor voltage under the following conditions:

- Voltage lower than specified - Closed loop - Above a specified TPS value - For a time longer than specified

Test Description: Step numbers refer to step numbers on diagnostic chart.

1. Checks to see if the condition is still present. A fixed dwell of under 10' indicates the problem is still present. A fixed dwell under 100 at idle, with dwell varying at 3000 rpm, usually indicates an intake leak. Check these areas prior to replacing the 02 sensor.

2. Checks to see if the ECM is able to respond to a rich condition caused by choking the engine. If it does, the problem is a lean engine condition, NOT electrical.

3. This step puts a rich 02 signal (about 1 volt) into Terminal "9" of the ECM. Dwell should increase (lean command).

4. If dwell increases to 45' with heavy choking the fault is an air leak, since the ECM was able to respond. If air is going to exhaust ports, disconnect the solenoid(s) for the air control valve. If air still goes to the ports, it is a faulty valve.

CODE 45 RICH EXHAUST INDICATION CARBURETED

Circuit Description:

Code 45 indicates that the ECM has seen:

- High oxygen sensor voltage - More than specified time (about 2 minutes) - Above a specified TPS value - Closed loop

A high voltage can be caused by a rich exhaust or 02 sensor contaminated with silicone.

Test Description: Step numbers refer to step numbers on diagnostic chart.

1. Checks to see if fault is still present. A dwell of under 45 degrees indicates engine should be checked for cause of intermittent rich condition: i.e.,

- Purge or bowl vent valves leaking. - Fuel in crankcase. - Fuel in evaporative canister. - Sticking mixture control solenoid or metering rods.

2. This step causes a lean condition by putting an air leak into the engine to see if ECM can respond. A drop in the dwell indicates ECM and 02 sensor are not faulty. Look for source of constant rich condition. See step one examples.

3. This step tests to see if ECM is able to respond to a lean exhaust 02 Signal (low voltage). If no dwell change with a grounded lead to 02 sensor Term. "9", fault is in ECM. It couldn't be an open 02 circuit because that would set Code 13.

4. This step checks the voltage from the ECM at the 02 sensor harness. Normal voltage at this point is the ECM bias voltage for no 02 signal which is approximately.45V. If voltage is high, CKT 412 to the ECM could be shorted to B +, or it is a faulty ECM.

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.