Code 34

AIR/FUEL RATIO "RICH" DURING OVERRUN FUEL CUTOFF - DTC 34

The ECM looks for the oxygen sensor feedback voltage to indicate a "rich" condition during overrun fuel cutoff.

During overrun fuel cutoff, the ECM checks the oxygen sensor raw voltage three times per engine revolution. Fuel cutoff occurs when the throttle is closed, engine speed is above 1100 rpm, and the coolant temperature is greater than 30°C (86°F).

The ECM will flag DTC 34 if the oxygen sensor feedback voltage indicates "rich" during overrun fuel cutoff for more than 32 consecutive checks.

Conditions Required For DTC 34 Flagging
Throttle position - At idle.
Engine speed - Greater than 2000 rpm.
Engine coolant temperature 34°C (94°F) or greater.
Oxygen sensor feedback voltage - 32 or more "rich" responses.
Response time 5 seconds.

Limp Home Default
None

Possible Faults
- Leaking fuel injector(s).
- Leaking/stuck purge valve.
- Leaking vacuum/pressure relief valve ("Rochester valve") diaphragm.

Diagnostic Notes
The oxygen sensor feedback voltage can be monitored and intermittent faults captured using the PDU "Datalogger" function. The PDU Datalogger can be set to trigger on flagging DTC 34.






Purge Valve Test
To Test For A Sticking Purge Valve
- Disconnect the purge hose at the intake manifold adapter.
- Switch ignition ON; do not start the engine.
- Apply vacuum to purge hose; vacuum should hold.
- If the vacuum does not hold, the purge valve is stuck and should be replaced.
- Switch ignition OFF; vacuum should release after a few seconds. If the vacuum does not release, the purge valve is stuck and should be replaced.

Flow Chart - DTC 34

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Flow Chart - DTC 34: