DTC 27

Code Chart 27:

Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION:

The ECM supplies a voltage of about 0.45 volt between terminals "OX2" and "OX1." (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volt). When the O2 sensor reaches operating temperature, it varies this voltage from about 0.1 volt (exhaust is lean) to about 0.9 volt (exhaust is rich). The sensor is like an open circuit and produces no voltage when it is below 360°C (600°F). An open sensor circuit, or cold sensor, causes open loop operation.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. Code 27 will set under the following conditions:

^ O2 signal voltage is steady between 1 volt or 0 volt.
^ Engine at normal operating temperature.
^ At least 2 minutes have elapsed since engine start-up.
^ All above conditions are met for about 60 seconds.

2. This test determines if the sub O2 sensor is the problem or if the ECM and wiring are at fault.

3. In doing this test, use only a 10 megaohm digital voltmeter. This test checks the continuity of the WHT wire and BLK wire. If BLK wire is open, the ECM voltage on WHT wire will be over 0.6 volt (600 mv).

DIAGNOSTIC AIDS:

Normal sub O2 sensor voltage varies between 0 mv to 999 mv (.1 and 1.0 volt) while in at normal operating temperature. Code 27 sets in one minute if sensor signal voltage remains between 0 volt or 1 volt. Verify a clean, tight ground connection for BLK wire. Open WHT wire or BLK wire will result in a Code 27. If Code 27 is intermittent, Testing and Inspection