Engine Control Module ECM

DTC 13 Chart:

Oxygen Sensor Circuit:

Circuit Description:
The ECM supplies a voltage of about .45 volt between terminals "D6" and "D7". (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volt.) The Oxygen Sensor (O2S) varies the voltage from a range of approximately 1 volt if the exhaust is rich, to approximately .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 .35 and .55 volt.

^ Throttle Position (TP) sensor signal above idle.

^ All conditions must be met for about 60 seconds.

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 ECM B fuse 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 CKTs 412 and 413, because if CKT 413 is open, the ECM voltage on CKT 412 will be over .6 volt (600 mV).

Diagnostic Aids: Normal scan tool voltage varies between 100 mV to 999 mV (.1 and 1.0 volt) while in "Closed Loop." DTC 13 sets in one minute if voltage remains between .35 and .55 volt; but the system will go "Open Loop" in about 15 seconds. Verify a clean tight ground connection for CKT 413. Open CKT 412 or CKT 413 will result in a DTC 13.