Diagnostic Aids
WARNING: This page is about a different car, the 2002 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
If DTC P0137 is also set, diagnose that DTC first. See DTC P0137: HO2S CIRCUIT - LOW VOLTAGE - SENSOR 2 .
DTC indicates engine is running lean in power enrichment mode. To verify system is running lean in power enrichment, use scan tool to monitor HO2S1 and HO2S2 under heavy acceleration. If both sensors are less than 300 millivolts, system is running lean and oxygen sensors are probably not at fault.
Possible causes of a lean air/fuel mixture are:
- Fuel pressure low/restricted fuel filter.
- Vacuum leak.
- Fuel quality poor or water/alcohol in fuel.
- Exhaust manifold gasket leak or leak around HO2S1.
- Fuel injectors clogged.
- HO2S1 weak.