For 1990-2009 cars

### 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 a 5 volt reference circuit, and provides a ground on a low reference circuit. The BARO sensor provides a voltage signal to the ECM on a signal circuit relative to the atmospheric pressure changes. The ECM monitors the BARO sensor signal for a voltage outside of the normal range. If the ECM detects a BARO sensor signal voltage that is too low, this DTC sets

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P2228 Barometric Pressure (BARO) Sensor Circuit Low Voltage

### Conditions for Running the DTC

• | The barometric pressure sensor start-up time is at least 2 seconds.

• | DTC P2228 runs continuously once the above conditions are met for 2 seconds.

### Conditions for Setting the DTC

• | The ECM detects that the BARO sensor voltage is less than 0.20 volts.

• | The condition is met for more than 4 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 4 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.

### Diagnostic Aids

• | Use the J 35616-A/BT-8637 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector.

• | The lower connector of the ECM is connector C1 and the upper connector of the ECM is connector C2. Refer to Engine Controls Component Views .

• | For an intermittent condition, refer to Intermittent Conditions .

### Test Description

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

1. This step determines if a condition exists.

2. This step is testing the signal circuit. The signal circuit is pulled up to a voltage, so the scan tool should display a voltage within the specified range. If the voltage is low, this indicates the signal circuit is grounded.

3. The ECM produces a measurable steady-state amperage that provides the 5 volt reference to the BARO sensor. If the amperage on the 5 volt reference circuit is less than the specified value, test the 5 -volt reference circuit for an open, a high resistance, or for a short to ground.

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 - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Turn the ignition switch to ON position, with the engine OFF.
2. Clear the diagnostic trouble codes (DTCs) with a scan tool.
3. Start the engine.
4. Observe the DTC information with a scan tool.

Does the DTC fail this ignition?

--

Go to Step 4

Go to Step 3

3 |

1. Observe the Freeze Frame/Failure Records for this DTC.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4 | Important: The signal circuit of the BARO sensor is pulled up to a voltage through a 1 mega-ohm resistor.

1. Turn OFF the ignition.
2. Disconnect the BARO sensor.
3. Turn the ignition switch to ON position, with the engine OFF.
4. Observe the BARO Volts parameter with a scan tool.

Is the voltage within the specified range?

4.9-5.2 V

Go to Step 5

Go to Step 7

5 |

1. Set-up a DMM to test amperage on the 400 mA scale.
2. Measure the amperage between the 5 volt reference circuit of the BARO sensor and the ECM housing with a DMM.

Is the amperage more than the specified value?

80 mA

Go to Step 8

Go to Step 6

6 |

1. Turn OFF the ignition.

Important: The 5 volt reference circuits are internally and externally connected at the controller. Other sensors that share the 5 volt reference circuit may also have DTCs set. Disconnecting a sensor on the shared 5 volt reference circuit may isolate a shorted sensor. Review the electrical schematic and diagnose the shared circuits and sensors.

2. Test the 5 volt reference circuit of the BARO sensor and all shared 5 volt reference circuits for an open, short to ground, or for high resistance. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 12

Go to Step 9

7 | Test the signal circuit of the BARO sensor for a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9
8 | Test for an intermittent and for a poor connection at the BARO sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10
9 | Test for an intermittent and for a poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11
10 | Replace the BARO sensor. Refer to Barometric Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 12 | --
11 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 12 | --
12 |

1. Clear the DTCs with a scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 13

13 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | System OK