: Service Emissions system message

07-02-10, 07:48 AM
I drove my '96 Seville the other day and the SERVICE - EMMISSIONS SYSTEM message displayed on the DIC so I pulled the codes.

PC 0138 CURRENT - HO2S circuit high voltage bank 1 sensor 2 (Pre-converter sensor)
PC 0151 CURRENT - HO2S Circuit low voltage bank 2 sensor 1 (sensor on front exhaust manifold)
PC 0154 HISTORY - Insufficient activity bank 2 sensor 1 (sensor on front exhaust manifold) This code was current a week ago.
PC 0174H Fuel trim system lean bank 2
PC 1599H Engine stall or near stall detected.

I'm thinking the oxygen sensor on the front exhaust manifold is starting to act flakey. I need to inspect the wiring. A flakey O2S on the front manifold might explain the PC 0151, 154 and 174 codes but not the 0138 code.

My wife said the car stalled on her a couple times earlier - that would explain the PC 1599 code.

I need to study the shop manual further but wondered if anyone had any ideas. I'd rather not replace $75 oxygen sensors until I know for sure that one is bad.

07-06-10, 07:36 PM
Suggest you check for vacuum leak(s)

07-11-10, 10:07 AM
Thanks for the suggestion. I'll have a look and see what I can find. The codes have not come back so I could be chasing a ghost...

08-01-10, 09:43 AM
I checked for vacuum leaks and could not find any. I cleared the codes and PC 0151 usually resets within 5 minutes of driving. I need to check the wiring, etc. to the front O2 sensor and see if there is something obviously wrong.

The shop manual states to check the snapshot data for long term fuel trim data for the front and rear banks. If both banks were lean, check for a condition that would cause a lean condition. This sounds like the manual is describing a vacuum leak.

There is a way to check the snapshot data via the onboard diagnostics somewhere in the shop manual...

08-01-10, 10:07 AM
That front (Bank 2) sensor's wiring runs pretty close to the exhaust manifold. With a circuit fault code you might want to check the sensor pigtail and connector for burnt insulation.

08-08-10, 05:23 PM
The front O2s wiring was well away from the exhaust manifold - nothing out of the ordinary was noticed there. I checked the intake manifold bolts and they were loose. I re-torqued them to 89 in-lbs. and took the car for a test drive and the PC0151 code set within 2 miles. I need to upgrade my scan tool to OBD-2 so I can monitor the O2s voltage per the PC0151 troubleshooting chart in the manual.

08-30-10, 12:18 PM
I could not locate any vacuum leaks and decided to replace the front O2 sensor. That fixed the problem.

08-30-10, 02:59 PM
Damn quirky cars..........thanks for the feedback.

I could not locate any vacuum leaks and decided to replace the front O2 sensor. That fixed the problem.