Powertrain Controls - ECM/PCM

DTC 45 Chart:

Left (Bank 2) Oxygen Sensor Circuit:

Circuit Description:
The Powertrain Control Module (PCM) supplies a voltage of about .45 volt between terminals "B21" and "B20." (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 45 Will Set When:
Vehicle is operating in "Closed Loop," CKT 1665 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 45 Will Clear When:
A current DTC 45 will clear when the O2S signal voltage falls below the calibrated rich exhaust voltage threshold. A history DTC 45 will clear after 50 consecutive ignition key cycles without a current DTC 45 being stored.

Diagnostic Aids:
Using the Tech 1 scan tool, observe the long term fuel trim values 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 45 may have been set. If the conditions for DTC 45 exist, the long term fuel trim values will be around 115.

- 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 45 may be set. Refer to "Fuel System Diagnosis," CHART A-7. Related Tests, Information and Procedures
- Rich injector. Perform "Injector/Coil Balance Test," CHART C-2A. Testing and Inspection
- Leaking injector. Refer to CHART A-7. Related Tests, Information and Procedures
- Crankcase oil. Check for fuel contaminated oil.
- 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 O2S signal indication). The PCM will then reduce the amount of fuel delivered to the engine, causing a severe surge driveability problem.
- An open round CKT 351 - May result in EMI, or induced electrical "noise." The PCM looks at 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 system to go rich. Engine tachometer will also show higher than actual engine speed, which can help in diagnosing this problem.
- EVAP canister purge. Check for fuel saturation. If full of fuel, check canister control and hoses.
- Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel.
- Throttle Position (TP) sensor. An intermittent Throttle Position (TP) sensor output will cause the system to go rich, due to a false indication of the engine accelerating.
- EGR. An EGR staying open (especially at idle) will cause the Oxygen Sensor (O2S) to indicate a rich O2S signal and this could result in a DTC 45.
- 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.