DTC P0108

Circuit Description

The barometric pressure sensor (BARO) responds to changes in altitude and atmospheric conditions. This gives the engine control module (ECM) an indication of barometric pressure. The ECM uses this information to calculate fuel delivery. The BARO sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The ECM supplies 5volts to the BARO sensor on the 5-volt reference2 circuit, and provides a ground on a low reference circuit. The BARO sensor provides a signal to the ECM on a signal circuit relative to the pressure changes. The ECM monitors the BARO sensor signal for voltage outside of the normal range. If the ECM detects a BARO sensor signal voltage that is excessively high, this diagnostic trouble code (DTC) will set.

Conditions for Running the DTC

The diagnostic runs continuously.

Conditions for Setting the DTC

The barometric pressure is more than 104kPa for 2seconds.

Action Taken When the DTC Sets

• / The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
• / The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

• / The control module turns OFF the malfunction indicator lamp (MIL) after 3consecutive ignition cycles that the diagnostic runs and does not fail.
• / A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
• / A history DTC clears after 40consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
• / Clear the MIL and the DTC with a scan tool.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step determines if the fault is actually on the 5-volt reference circuit or if the fault is from a short to battery voltage back feeding from the signal circuit of the BARO sensor.
  1. This step inspects the ECM and the electrical connector for possible bent pins or any unwanted circuit to circuit contact.

Step / Action / Values / Yes / No
1 / Did you perform the Diagnostic System Check-Engine Controls? / -- / Go to Step2 / Go to Diagnostic System Check - Engine Controls
2 /
  1. Start the engine.
  2. Using the scan tool, monitor the Diagnostic Trouble Code (DTC) information.
Does the scan tool indicate that DTC P1639 is current? / -- / Go to Step3 / Go to Step4
3 /
  1. Turn OFF the ignition.
  2. Disconnect the BARO sensor electrical connector.
  3. Turn the ignition ON, with engine OFF.
Does the scan tool indicate that the BARO sensor pressure is less than the specified value? / 45kPa / Go to DTC P1639 / Go to Step6
4 /
  1. Turn OFF the ignition.
  2. Disconnect the BARO sensor electrical connector.
  3. Turn the ignition ON, with the engine OFF.
  4. Measure the voltage from the signal circuit of the BARO sensor to a good ground.
Does the voltage measure more than the specified value? / 0.5V / Go to Step5 / Go to Step8
5 / Test the signal circuit of the BARO sensor for a short to 5volts.
Did you find and correct the condition? / -- / Go to Step10 / Go to Step7
6 / Test the signal circuit of the BARO sensor for a short to battery voltage.
Did you find and correct the condition? / -- / Go to Step10 / Go to Step7
7 / Inspect for poor connections at the ECM.
Did you find and correct the condition? / -- / Go to Step10 / Go to Step9
8 / Replace the BARO sensor. .
Did you complete the replacement? / -- / Go to Step10 / --
9 / Replace the ECM.
Did you complete the replacement? / -- / Go to Step10 / --
10 /
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC run and pass? / -- / Go to Step11 / Go to Step2
11 / With a scan tool, observe the stored information, Capture Info.
Does the scan tool display any DTCs that you have not diagnosed? / -- / Go to Diagnostic Trouble Code (DTC) List / System OK

Barometric Pressure Sensor Replacement

Removal Procedure

  1. Turn OFF the ignition.


  1. Disconnect the BARO sensor electrical connector (1).


  1. Bend the locking tab (2), located on the bracket, away from the sensor, just enough so that the sensor will pass.
  2. Pull the BARO sensor (3) downward to remove it from the bracket.