Applicable Systems
OBD-II
Symptoms
O2 sensor signal stuck lean (low voltage); ECM enriches mixture; poor fuel economy; possible vacuum leak.
Possible Causes
- O2 sensor signal wire short to ground
- Vacuum leak causing lean condition
- O2 sensor lazy response
Troubleshooting Steps
- Step 1: Check O2 sensor signal wire for short to ground
No short to ground - Step 2: Perform smoke test for vacuum leaks
No leaks found - Step 3: Monitor O2 sensor switching on scanner
Sensor switches 0.1-0.9V - Step 4: Check fuel trim values (STFT/LTFT)
Trims within +/- 10% - Step 5: Replace O2 sensor if signal stuck low
New sensor signal switches
How to Reset
Clear with OBD-II scanner after repair; verify fuel trims.
Common Replacement Parts
- O2 Sensor Bank 1 Sensor 1 (OEM spec)
Frequently Asked Questions
- Q: What voltage is lean vs rich for O2 sensor?
0.1-0.4V = lean, 0.5-0.9V = rich. Sensor should switch between lean and rich 2-5 times per second in closed loop.
Source: SAE J2012 standard DTC list + OBD-II portal
Category: OBD-II