P063A-Generator voltage sense circuit

P063A code - theory of operation, the Powertrain Control Module (PCM) uses the Generator field duty cycle signal circuit or F-terminal circuit, to monitor the duty cycle of the generator. The Generator field duty cycle signal circuit connects to high side of the field windings in the Generator. A pulse Widht Modulated (PWM) high side driver in the voltage regulator turns the field warnings ON and OFF. The PCM uses the PWM signal input to determine the Generator load on the engine. This allows the PCM to adjust the idle speed to compensate for high electrical loads. The PCM monitors the status of the generator field duty cycle signal circuit. When the key is in the RUN position and the engine is OFF, the PCM should detect a duty cycle near 0 percent. However, when the engine is running, the duty cycle should be between 5-95 percent.

When monitored This diagnostic runs one time during an ignition cycle with the engine running. Set condition the Alternator sense circuit voltage is less than the Battery feed circuit voltage. Default actions the battery light will illuminate, the MIL light will illuminate, the fault will be checked again on the next key cycle.

Possible causes P063A code:

• Alternator sense circuit open/high resistance.
• Alternator sense circuit shorted to ground.
• Alternator.
• Powertrain Control Module (PCM).

Diagnose code P063A-Generator voltage sense circuit

Step 1. Check for an active DTC
Inspect and test the Battery with the Midtronics Battery Tester or equivalent for a shorted or dead cell before continuing with the test. The Alternator belt and tensioner condition must be checked before continuing. Start the engine, allow the idle to stabilize. With the scan tool, read DTC.

Is the DTC active or pending ?

Yes, go to step 2.

No, perform the PCM intermittent condition.

Step 2. Check the Alternator sense circuit for an open/high resistance

Turn the ignition off, disconnect the alternator harness connector and disconnect the PCM harness connector. Measure the resistance of the Alternator sense circuit between the Alternator harness connector and PCM connector.

Is the resistance below 3.0 Ohms ?

Yes, go to step 3.

No, repair the Alternator sense circuit for an open or high resistance.

Step 3. Check the Alternator sense circuit for a short to ground

Check for continuity between ground and the Alternator sense circuit at the Alternator harness connector.

Is there continuity between ground and the Alternator sense circuit ?

Yes, repair the Alternator sense circuit for a short to ground.

No, go to step 4.

Step 4. Alternator Operation

Reconnect the Alternator harness connector, reconnect the PCM harness connector. Start the engine, measure the voltage at the Alternator output stud. Probe and measure the voltage of the Alternator sense circuit at the PCM harness connector.

The Alternator sense circuit  reading will normally be approximately 3.5 volts less than the voltage at the Alternator output terminal due to an internal resistor inside the Alternator.

Does the voltage read as described above ?

Yes, go to step 5.

No, verify that there is good pin to terminal contact in the Alternator and Powertrain Control Module (PCM) connectors. Replace the Alternator if no problems were found with the connectors.

Step 5. Check related PCM and component connections

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