P0129-BAROMETRIC PRESSURE OUT-OF-RANGE LOW

For a complete wiring diagram Refer to Section 8W.

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. MIL is illuminated and the 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 THE (K900) SENSOR GROUND

MAP SENSOR

PCM

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).

Diagnostic Test

1.ACTIVE DTC

Is the DTC Active at this time.

Yes

Go To 2

Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

2.(F856) 5-VOLT SUPPLY CIRCUIT

Is the voltage between 4.5 to 5.2 volts?

Yes

Go To 3

Go To 7

3.MAP SENSOR

Is the voltage above 2.2 volts?

Yes

Replace the MAP Sensor.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

Go To 4

4.(K1) MAP SIGNAL CIRCUIT OPEN

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.

Is the resistance below 5.0 ohms?

Yes

Go To 5

Repair the open in the (K1) MAP Signal circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

5.(K1) MAP SIGNAL CIRCUIT SHORTED TO THE (K900) SENSOR GROUND CIRCUIT

Is the resistance below 5.0 ohms?

Yes

Repair the short between the (K900) Sensor ground circuit and the (K1) MAP Signal circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

Go To 6

6.(K1) MAP SIGNAL CIRCUIT SHORTED TO GROUND

Is the resistance below 100 ohms?

Yes

Repair the short to ground in the (K1) MAP Signal circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

Go To 10

7.(F856) 5-VOLT SUPPLY CIRCUIT SHORTED TO BATTERY VOLTAGE

Is the voltage above 5.2 volts?

Yes

Repair the short to battery voltage in the (F856) 5-volt Supply circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

Go To 8

8.(F856) 5-VOLT SUPPLY CIRCUIT OPEN

Is the resistance below 5.0 ohms?

Yes

Go To 9

Repair the open in the (F856) 5-volt Supply circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

9.(F856) 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND

Is the resistance below 100 ohms?

Yes

Repair the short to ground in the (F856) 5-volt Supply circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

Go To 10

10.PCM

NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.

Were there any problems found?

Yes

Repair as necessary.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

Replace and program the Powertrain Control Module per Service Information.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)