P0129
SYMPTOM
P0129-BAROMETRIC PRESSURE OUT-OF-RANGE LOW
WHEN MONITORED
With the ignition key on. No Cam or Crank signal within 75 ms. Engine speed less than 250 RPM.
SET CONDITION
The PCM senses the voltage from the MAP sensor to be less than 2.2 volts but above 0.04 of a volt for 300 milliseconds. One Trip Fault. Three good trips to turn off the MIL. (5.7L ETC lamp will flash)
POSSIBLE CAUSES
- (F856) 5-VOLT SUPPLY CIRCUIT SHORTED TO BATTERY VOLTAGE
- (F856) 5-VOLT SUPPLY CIRCUIT OPEN
- (F856) 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
- (K1) MAP SIGNAL CIRCUIT OPEN
- (K1) MAP SIGNAL CIRCUIT SHORTED TO GROUND
- (K1) MAP SIGNAL CIRCUIT SHORTED TO (K900) SENSOR GROUND
- MAP SENSOR
- PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Scan Tool Testing and Procedures
DIAGNOSTIC TEST
1. ACTIVE DTC
Ignition on, engine not running. With a scan tool, read DTCs.
Is the DTC active at this time.
Yes>> Go To 2
No>> Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5. Powertrain Verification Test - Ver 5
2. (F856) 5-VOLT SUPPLY CIRCUIT
Turn the ignition off.
Disconnect the MAP Sensor harness connector.
Ignition on, engine not running.
Measure the voltage on the (F856) 5-volt Supply circuit in the MAP Sensor harness connector.
Is the voltage between 4.5 to 5.2 volts?
Yes>> Go To 3
No>> Go To 7
3. MAP SENSOR
With a scan tool, monitor the MAP Sensor voltage with the Sensor harness connector disconnected.
Is the voltage above 2.2 volts?
Yes>> Replace the MAP Sensor. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Go To 4
4. (K1) MAP SIGNAL CIRCUIT OPEN
Turn the ignition off. Disconnect the PCM harness connectors.
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. Install Miller Special Tool # 8815 to perform diagnosis.
Measure the resistance of the (K1) MAP Signal circuit from the MAP Sensor harness connector to the appropriate terminal of special tool # 8815.
Is the resistance below 5.0 ohms?
Yes>> Go To 5
No>> Repair the open in the (K1) MAP Signal circuit. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
5. (K1) MAP SIGNAL CIRCUIT SHORTED TO THE (K900) SENSOR GROUND CIRCUIT
Measure the resistance between the (K900) Sensor ground circuit and the (K1) MAP Signal circuit in the MAP Sensor harness connector.
Is the resistance below 5.0 ohms?
Yes>> Repair the short between the (K900) Sensor ground circuit and the (K1) MAP Signal circuit. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Go To 6
6. (K1) MAP SIGNAL CIRCUIT SHORTED TO GROUND
Measure the resistance between ground and the (K1) MAP Signal circuit in the MAP Sensor harness connector.
Is the resistance below 100 ohms?
Yes>> Repair the short to ground in the (K1) MAP Signal circuit. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Go To 10
7. (F856) 5-VOLT SUPPLY CIRCUIT SHORTED TO BATTERY VOLTAGE
Turn the ignition off.
Disconnect the PCM harness connectors.
Ignition on, engine not running.
Measure the voltage on the (F856) 5-volt Supply circuit in the MAP Sensor harness connector.
Is the voltage above 5.2 volts?
Yes>> Repair the short to battery voltage in the (F856) 5-volt Supply circuit. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Go To 8
8. (F856) 5-VOLT SUPPLY CIRCUIT OPEN
Turn the ignition off.
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. Install Miller Special Tool # 8815 to perform diagnosis.
Measure the resistance of the (F856) 5-volt Supply circuit from the MAP Sensor harness connector to the appropriate terminal of special tool # 8815.
Is the resistance below 5.0 ohms?
Yes>> Go To 9
No>> Repair the open in the (F856) 5-volt Supply circuit. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
9. (F856) 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
Measure the resistance between ground and the (F856) 5-volt Supply circuit in the MAP Sensor harness connector.
Is the resistance below 100 ohms?
Yes>> Repair the short to ground in the (F856) 5-volt Supply circuit. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Go To 10
10. PCM
Note: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.
Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.
Were there any problems found?
Yes>> Repair as necessary. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Replace and program the Powertrain Control Module per Service Information. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.