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Home >> Buick >> 2007 >> Lucerne CX >> Repair and Diagnosis >> External Pages >> Different car >> Section 231 (Engine Controls - 3.9L - DTC P0442 To P2A01) >> DTC P0641 or P0651 >> Circuit/System Testing

Circuit/System Testing

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P0641

  1. Disconnect the MAP sensor electrical connector.
  2. With the ignition ON and the engine OFF, measure for 4.8-5.2 volts from the 5-volt reference circuit of the MAP sensor to ground with a DMM.
    • If the voltage is more than 5.2 volts, test for a short to voltage on the 5-volt reference circuits of all the sensors connected to the 5-volt reference A bus, a short to voltage on the FTP sensor signal circuit or a faulty control module.
    • If the voltage is less than 4.8 volts, test for a short to ground on the 5-volt reference circuits of all the sensors connected to the 5-volt reference A bus or a faulty control module.
  3. Measure the voltage from the 5-volt reference circuit of the MAP sensor to ground. Monitor the DMM while disconnecting all other sensors connected to the 5-volt reference A bus, one at a time.
    • If the voltage returns to 4.8-5.2 volts when a sensor is disconnected, replace the applicable sensor.
  4. Reconnect all sensors except the EOP sensor.
  5. Measure for 4.8-5.2 volts from the 5-volt reference circuit of the EOP sensor to ground with a DMM.
    • If the voltage is not within 4.8-5.2 volts, test for a short to voltage on the MAP sensor signal circuit or a faulty MAP sensor.

P0651

  1. Disconnect the throttle body electrical connector.
  2. With the ignition ON and the engine OFF, measure for 4.8-5.2 volts from the 5-volt reference circuit to ground with a DMM.
    • If the voltage is more than 5.2 volts, test for a short to voltage on the 5-volt reference circuits of APP sensor 1 and TP sensor 1 and 2 or for a faulty control module.
    • If the voltage is less than 4.8 volts, test for a short to ground on the 5-volt reference circuits of APP sensor 1 and TP sensor 1 and 2 or a faulty control module.
  3. Continue to measure the voltage from the 5-volt reference circuit of the throttle body electrical connector to ground. Monitor the DMM while disconnecting APP sensor 1.
    • If the voltage returns to 4.8-5.2 volts when APP sensor 1 is disconnected, replace the APP sensor.
  4. Connect the throttle body electrical connector.
  5. With the ignition ON and the engine OFF, measure for 4.8-5.2 volts from the 5-volt reference circuit to ground with a DMM.
    • If the voltage is not within 4.8-5.2 volts, replace the throttle body assembly.
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