DTC 25

Code 25:

CIRCUIT DESCRIPTION:

The ECM supplies a voltage of about 0.45 volt between terminals "OX" and "E1." (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 25 is set when the O2 sensor signal voltage on BLACK wire remains below 0.2 volt for 60 seconds or more and the system is operating in "CLOSED LOOP."

DIAGNOSTIC AIDS:

^ O2 Sensor Wire. Sensor pigtail may be mis-positioned and contacting the exhaust manifold. Check for ground in wire between connector and sensor.

^ Fuel Contamination, Water, even in small amounts, near the in-tank fuel pump inlet can be delivered to the injector. The water causes a lean exhaust and can set a Code 25.

^ Fuel Pressure System, will be lean if fuel pressure is too low. It may be necessary to monitor fuel pressure while driving the car at various road speeds and/or loads to confirm.

^ Exhaust Leaks. If there is an exhaust leak, the engine can cause outside air to be pulled into the exhaust and past the sensor. Vacuum or crankcase leaks can cause a lean condition.

^ If Code 25 is intermittent, see Diagnosis by Symptoms.