Fault Code 51


Description:  Oxygen sensor output indicates lean too long
Power loss light:  Off
Limp-in mode:  Engine allowed to run rich, but prevented from running lean

Possible Causes

Bad oxygen sensor - Replace the sensor which is located on the turbo housing near the down pipe (for turbo) or on the down pipe near the exhaust manifold.

Bad connection or wiring - Check the wiring and connections between the sensor and the logic module (or SMEC).  Clean and regrease any corroded connectors with dielectric grease and repair any shorts.  Look for melted wire insulation near the exhaust manifold.  A shorted connection to ground or any positive source will cause this fault code.

Low fuel rail pressure - See the Diagnosing Your Fuel System page.

Diagnostic Method

Trigger Parameters

- In closed-loop
- Sensor output indicates lean for more than 715 seconds (11 minutes, 55 seconds)

Results If Component Fails

A fault code 51 is stored, the circuit stays in closed-loop, and the logic module will still monitor the oxygen sensor signal.  If the condition persists for four times what it took to set the code, the logic module will allow the engine to run rich, but prevent it from running lean.
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This page is maintained by Russell W. Knize and was last updated 08/28/98. Comments? Questions? Send email.

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