Engine - Runs Rough, Surges at Idle, Stalls After Start: Overview
BULLETIN NO.: 96-T-32AISSUE DATE: April, 1997
GROUP/SEQ. NO.: Engine-09
CORPORATION NO.: 686506R
SUBJECT:
Engine Runs Rough, Surges at Idle, Stalls after Start and/or MIL On and PCM/EC DTC 45 (1995 Vehicles) or DTC P0172 (1996 Vehicles) (Replace O2S Wire)
This bulletin is being revised to add a part number for the replacement wire and supercedes bulletin 96-T-32, which should be discarded. Revisions are shown by asterisks.
MODELS AFFECTED:
1995 Saturns built between and including VINs SZ352000 and SZ403344, and 1996 Saturns built between VINs TZ100181 and TZ143882.
CONDITION:
Engine may run rough or surge at idle, or the engine may start then stall. In some cases, the malfunction indicator lamp (MIL) (SERVICE ENGINE SOON telltale lamp) may be On with PCM/EC diagnostic trouble code (DTC) 45 (1995 vehicles) or DTC P0172 (1996 vehicles) stored in memory. DTC 45 (Rich Oxygen Sensor Signal) or DTC P0172 (Learned Fuel Control Fuel System Too Rich) indicates that the oxygen sensor is sensing a rich fuel condition.
The conditions stated above may occur when:
^ Driving through precipitation containing road salts.
^ Driving through standing water containing road salts.
^ Driving through precipitation after the vehicle has been subjected to road salts.
^ During or after a car wash.
CAUSE:
The oxygen sensor (Purple) wire for circuit 412 may have perforations in the insulation causing intermittent malfunction of the oxygen sensor signal. These perforations are only visible with magnification.
CORRECTION:
Refer to Procedures in this bulletin to diagnose this condition.
PROCEDURES
Diagnosis
The oxygen sensor (O2S) consists of a zirconia electrolyte between two platinum plates. When the sensor reaches approximately 318°C (600°F) it becomes an electrical source that responds to the oxygen content in the exhaust. The PCM produces a bias voltage of approximately 450 millivolts on the oxygen sensor circuit. When the sensor is cold, its internal resistance is extremely high, therefore, the PCM recognizes the bias as an open circuit. As the sensor warms up, the internal resistance decreases. When the sensor reaches approximately 318°C (600° F), it starts producing a voltage based on the oxygen content in the exhaust stream. This voltage is used by the PCM to determine a rich or lean oxygen sensor signal and adjusts the fuel mixture accordingly.
DIAGNOSTIC AIDS
1. Bias voltage of less than 600 mV should be observed with oxygen sensor disconnected. If higher voltage is observed, the source must be diagnosed.
2. Turning On cooling fans may provide the voltage source for oxygen sensor short.
3. Oxygen sensor wire perforation results in short to voltage through conductive salt water. If harness was exposed to salt water in the past, wetting the harness will "reactivate" the salt water short.
4. If the voltage on oxygen sensor wire is less than 600 mV, refer to service manual for appropriate symptom diagnosis.
PARTS REQUIREMENTS:
21022282 Connector Kit-Oxygen Sensor (1 required)
21022987 Sensor Asm-Exhaust Oxygen (1, if required)
21020792 Strap-Wiring Harness (10 required)
21023494 Conduit-Wiring Harness (1.5 meters [5 ft.] required.)
IMPORTANT:
Conduit is packaged in a 3 meter (10 ft.) length package. One package is to be used for two vehicles.
12116140 0.80 sq. mm (18 gauge) stranded copper wire with GXL insulation (2.75 meters [9 ft.] required)
Crimp and Seal Splice (Salmon/Pink)
OTC P/N 217670 (2 required)
CLAIM INFORMATION:
To receive credit for this repair during the warranty coverage period, submit a claim through the Saturn Dealer System as shown:
Labor
Case Operation
Type Description Code Time
VW Replace Oxygen Sensor Wire T9704 1.2 hrs