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 low, 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 less than 45 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.
-
The BARO sensor 5-volt reference circuit is shared with other sensors. If DTC P1639 is set, this indicates that the 5-volt reference circuit is either shorted to ground or shorted to voltage and should be diagnosed first. The short may be on another sensor 5-volt reference circuit.
-
Operate the vehicle within the same conditions as when the DTC failed. If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data can aid in locating an intermittent condition.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
Does the scan tool indicate that DTC P1639 is current? | -- | Go to DTC P1639 | Go to Step 3 | |
3 | With a scan tool observe the BARO sensor pressure. Does the scan tool indicate that the pressure is less than the specified value? | 45 kPa | Go to Step 5 | Go to Step 4 |
Does the DTC fail this ignition? | -- | Go to Step 5 | Go to Intermittent Conditions | |
5 |
Does the voltage measure near the specified value? | 5 V | Go to Step 6 | Go to Step 7 |
6 | Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the BARO sensor and the signal circuit of the BARO sensor. Does the scan tool indicate that the BARO sensor pressure is more than the specified value? | 103 kPa | Go to Step 9 | Go to Step 8 |
7 | Test the 5 volt reference circuit of the BARO sensor for an open. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 |
8 | Test the signal circuit of the BARO sensor for a short to ground, low reference, or an open. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 |
9 | 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 13 | Go to Step 11 |
10 | 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 13 | Go to Step 12 |
11 | Replace the BARO sensor. Refer to Barometric Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- |
12 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- |
13 |
Does the DTC run and pass? | -- | Go to Step 14 | Go to Step 2 |
14 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
