Circuit Description
The barometric pressure (BARO) sensor 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 5 volts to the BARO sensor on the 5-volt reference 2 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 DTC will set.
Conditions for Running the DTC
The engine is running.
Conditions for Setting the DTC
The BARO is more than 110 kPa for 2 seconds.
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 3 consecutive 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 40 consecutive 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.
-
A short to voltage on the 5-volt reference circuit will cause DTC P1639 to set.
-
This step tests the signal circuit of the BARO sensor for a short to voltage. The short may backfeed through the sensor to the 5- volt reference circuit causing the DTC P1639 to set.
-
This step tests the signal circuit of the boost sensor for a short to voltage. The short may backfeed through the sensor to the 5-volt reference circuit causing the DTC P1639 to set.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
2 |
Does the scan tool indicate that the pressure is more than the specified value? | 110 kPa | Go to Step 4 | Go to Step 3 |
3 |
Does the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions |
Monitor the diagnostic trouble code (DTC) information with a scan tool. Does the scan tool indicate that DTC P1639 is current? | -- | Go to Step 7 | Go to Step 5 | |
5 |
Does the scan tool indicate that the BARO sensor pressure is less than the specified value? | 44 kPa | Go to Step 6 | Go to Step 9 |
6 |
Does the test lamp illuminate brightly? | -- | Go to Step 13 | Go to Step 12 |
Does the scan tool indicate that the BARO sensor pressure is less than the specified value? | 44 kPa | Go to Step 8 | Go to Step 10 | |
Disconnect the electrical connector of the boost sensor. Refer to Boost Sensor Replacement . Does the scan tool indicate that the boost sensor pressure is less than the specified value? | 50 kPa | Go to DTC P1639 | Go to Step 11 | |
9 | Test the signal circuit of the BARO sensor for a short to 5 volts. Refer to Testing for a Short to Voltage and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 16 |
10 | Test the signal circuit of the BARO sensor for a short to battery voltage. Refer to Testing for a Short to Voltage and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 16 |
11 | Test the signal circuit of the Boost sensor for a short to battery voltage. Refer to Testing for a Short to Voltage and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 16 |
12 | Test the low reference circuit of the BARO sensor for high resistance or an open. Refer to Circuit Testing in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 14 |
13 | Inspect for poor connections at the BARO sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 15 |
14 | Inspect for poor connections at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 16 |
15 | Replace the BARO sensor. Refer to Barometric Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 17 | -- |
16 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 17 | -- |
17 |
Does the DTC run and pass? | -- | Go to Step 18 | Go to Step 2 |
18 | Observe the stored information, Capture Info., with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
