Powertrain Controls - ECM/PCM

DTC 65 Chart:

Right (Bank 1) Oxygen Sensor Circuit:

Circuit Description:
The Powertrain Control Module (PCM) supplies a voltage of about .45 volt between terminals "B22" and "B23." (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volt.)

When the O2S reaches operating temperature, it varies this voltage from about 100 millivolts (exhaust is lean) to about 900 millivolts (exhaust is rich).

The sensor is like an open circuit and produces no voltage when it is below 316°C (600°F). An open sensor circuit or cold sensor causes "Open Loop" operation.

DTC 65 Will Set When:
Vehicle is operating in "Closed Loop," CKT 1666 is above 750 millivolts, throttle angle is between 6% and 20% condition present for greater than 60 seconds.

Action Taken (PCM will default to):
Vehicle will operate in "Open Loop" and MIL will become illuminated.

DTC 65 Will Clear When:
A current DTC 65 will clear when the O2S signal voltage falls below the calibrated rich exhaust threshold. A history DTC 65 will clear after 50 consecutive ignition key cycles without a current DTC 45 being stored.

Diagnostic Aids:
Using the Tech scan tool, observe the long term fuel trim value at different RPM and air flow conditions. The Tech 1 scan tool also displays the fuel trim cells, so the long term fuel trim values can be checked in each of the cells to determine when the DTC 65 may have been set. If the conditions for DTC 65 exists, the long term fuel trim values will be around 115 or lower.

Check the following possible causes:

- Fuel Pressure - System will go rich, if pressure is too high. The PCM can compensate for some increase. However, if it gets too high, a DTC 65 will be set. Refer to "Fuel System Diagnosis," CHART A-7. Related Tests, Information and Procedures
- Leaking fuel injector(s) - Refer to CHART A-7.
- An open ground CKT 351 - May result in induced electrical "noise." The PCM interprets this "noise" as reference pulses. The additional pulses result in a higher than actual engine speed signal. The PCM then delivers too much fuel causing the system to go rich. The engine tachometer will also show higher than actual engine speed, which can help in diagnosing this problem.
- Canister Purge - Check for fuel saturation. If fuel vapor canister is full of fuel, check EVAP canister control valve and hoses.
- MAP sensor - An output that causes the PCM to sense a higher than normal manifold pressure (low vacuum) can cause the system to go rich. Disconnecting the Manifold Absolute Pressure (MAP) sensor will allow the PCM to set a fixed value for the MAP sensor. Substitute a different MAP sensor if the rich condition is gone, while the sensor is disconnected.
- TP sensor - An intermittent Throttle Position (TP) sensor output will cause the system to operate richly due to a false indication of the engine accelerating.
- O2S contamination - Inspect Oxygen Sensor (O2S) for silicone contamination from fuel, or use of improper RTV sealant. The sensor may have a white, powdery coating and result in a high but false signal voltage (rich exhaust indication). The PCM will then reduce the amount of fuel delivered to the engine causing a severe surge driveability problem.
- EGR valve - Exhaust Gas Recirculation (EGR) sticking open idle is usually accompanied by a rough idle and/or stall condition.
- If DTC 65 is intermittent, refer to "Diagnosis By Symptom." Testing and Inspection
- Engine oil contamination - Fuel fouled engine oil could cause the O2S to sense a rich air/fuel mixture and set a DTC 65.