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DTC P0129: Barometric Pressure Out-Of-Range Low: Testing

  1. Turn ignition on, engine not running. With the DRBIII®, read DTCs and record related Freeze Frame data. Is the Good Trip counter displayed and equal to zero? If yes, go to next step. If no, go to step  11.
  2. Turn the ignition off. Disconnect the MAP Sensor harness connector. Turn ignition on, engine not running. Measure the voltage of the 5-Volt Supply circuit in the MAP Sensor harness connector. Is the voltage between 4.5 and 5.2 volts? If yes, go to next step. If no, go to step  7.
  3. With the DRBIII®, monitor the MAP Sensor voltage. Is the voltage above 2.2 volts? If yes, replace the MAP Sensor. If no, go to next step.
    4. CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal-to-pin connection. Use Miller Special Tool (8815) when performing diagnosis at PCM harness connectors.
  4. Turn the ignition off. Disconnect the PCM harness connectors. Measure the resistance of the MAP Sensor Signal circuit from the MAP Sensor harness connector to the appropriate terminal of the Miller Special Tool. Is the resistance below 5.0 ohms? If yes, go to next step. If no, repair the open in the MAP Sensor Signal circuit.
  5. Measure the resistance between ground and the MAP Sensor Signal circuit at the MAP Sensor harness connector. Is the resistance below 100 ohms? If yes, repair the short to ground in the MAP Sensor Signal circuit. If no, go to next step.
    6. NOTE: Before continuing, check the PCM harness connectors for corrosion, damage or terminal push out. Repair as necessary.
  6. There are no possible causes remaining, replace PCM. Program the new PCM. See PROGRAMMING .
  7. Measure the voltage of the 5-Volt Supply circuit in the MAP Sensor harness connector. Is the voltage above 5.2 volts? If yes, repair the short to voltage in the 5-Volt Supply circuit. If no, go to next step.
  8. Turn the ignition off. Disconnect the PCM harness connectors. Measure the resistance between ground and the 5-Volt Supply circuit at the MAP Sensor harness connector. Is the resistance less than 100 ohms? If yes, repair the short to ground in the 5-Volt Supply circuit. If no, go to next step.
    9. CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal-to-pin connection. Use Miller Special Tool (8815) when performing diagnosis at PCM harness connectors.
  9. Measure the resistance of the 5-Volt Supply circuit from the MAP Sensor harness connector to the appropriate terminal of the Miller Special Tool. Is the resistance below 5.0 ohms? If yes, go to next step. If no, repair the open in the 5-Volt Supply circuit.
    10. NOTE: Before continuing, check the PCM harness connectors for corrosion, damage or terminal push out. Repair as necessary.
  10. There are no possible causes remaining, replace PCM. Program the new PCM. See PROGRAMMING .
  11. Start the engine. Allow engine to idle. If the engine will not idle, maintain an engine speed between 800 and 1500 RPM. With the DRBIII®, read the IAC Current. Is the IAC Current below 146 mA? If yes, go to DTC P0508: IAC VALVE SENSE CIRCUIT LOW . If no, go to next step.
  12. Start the engine. Allow engine to idle. If the engine will not idle, maintain an engine speed between 800 and 1500 RPM. With the DRBIII®, read the IAC Current. Is the IAC Current above 999 mA? If yes, go to DTC P0509: IAC VALVE SENSE CIRCUIT HIGH . If no, go to next step.
    13. WARNING: When the engine is operating, do not stand in a direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing.
  13. The conditions that set the DTC are not present at this time. The following may help in identifying the intermittent condition. With the engine running at normal operating temperature, monitor the DRBIII® parameters related to the DTC while wiggling the wiring harness. Look for parameter values to change and/or a DTC to set. Review the DRBIII® Freeze Frame information. If possible, try to duplicate the conditions under which the DTC was set. Refer to any Technical Service Bulletins (TSB) that may apply. Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or partially broken wires. Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals. Look for parameter values to change and/or a DTC to set. Were any of the above conditions present? If yes, repair as necessary. If no, test is complete.
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