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P0138, P0140

Read the instructions below then start the fault diagnostic procedure.

Symptom: CHECK ENGINE lamp on.

P0138, P0140


Rear Heated Oxygen Sensor. Short to B+

Rear Heated Oxygen Sensor Circuit. Short to Ground / Open circuit.


Fault symptoms

CHECK ENGINE lamp on.

Conditions

P0138: Ignition ON: sensor voltage >1500 mV for longer than 5 sec.

P0140: Diagnosis not yet performed during this trip.


• Car moving.

• Engine coolant temperature >70C (>158F).

• Oxygen sensor voltage has not exceeded 0.4 V and has not changed more than 0.5 V within 500 sec.


Diagnostic help

The function of the oxygen sensor can be read with the diagnostic tool.


- Select " Data Display".



- Select " O2S 2".


With full load, the diagnostic tool should show >0.7 V and approx. 0 V with fuel shut-off.

Both P0132 and P0138 are often generated if any of the oxygen sensor reference grounds or sensor voltage is short-circuited to B+ in the wiring harness or in any of the oxygen sensors.

The oxygen sensor control module inputs are high-ohmic. A diagnostic trouble code will be generated if moisture enters any of the oxygen sensor connectors.

Checking the wiring harness. Intermittent faults may occur in connection with short circuits and open circuits. Jiggle the wiring harness at several points and in several directions to locate any problems in the wiring, including intermediate connectors. Observe the multimeter, scan tool or test lamp during the check.