Engine Control Module ECM

Diagnostic Trouble Code 13:

Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION
The ECM supplies a voltage of about 0.45 volt between terminals "D6" and "D7." (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volt.) The Oxygen Sensor (O2S) varies the voltage from a range of approximately 1 volt if the exhaust is rich, to approximately 0.10 volt if exhaust is lean.

The sensor is like an open circuit and produces no voltage when it is below approximately 315°C (600°F). An open sensor circuit or cold sensor causes "Open Loop" operation.

DTC 13 WILL SET WHEN
^ Engine temperature greater than 70°C (158°F).
^ Two minutes engine time after start.
^ O2S signal voltage steady between 0.35 and 0.55 volt.
^ Throttle Position (TP) sensor signal above 9%.
^ All conditions must be met for about 2 minutes.

ACTION TAKEN (ECM WILL DEFAULT TO)
The Malfunction Indicator Lamp (MIL) will illuminate, and the system will go "Open Loop."

DTC 13 WILL CLEAR WHEN
Conditions for fault are no longer present and Tech 1 "Clear DTCs" function is used or 50 ignition switch keycycles have passed with no further faults or ignition switch is turned "OFF" and battery feed voltage is removed for 10 seconds.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Verifies DTC criteria.

2. This will determine if the sensor is at fault or the wiring or ECM is the cause of DTC 13.

3. In doing this test, use only a high impedance digital volt ohmmeter. This test checks the continuity of the O2S signal and the O2S sensor ground circuits, because if the O2S sensor ground circuit is open, the ECM voltage on O2S signal circuit will be over 0.6 volt (600 mV).

DIAGNOSTIC AIDS
Normal scan tool voltage varies between 100 mV to 999 mV (0.1 and 1.0 volt) while in "Closed Loop." DTC 13 sets in one minute if voltage remains between 0.35 and 0.55 volt; but the system will go "Open Loop" in about 15 seconds. Verify a clean tight ground connection for the O2S sensor ground circuit. Open O2S signal or O2S sensor ground circuits will result in a DTC 13.