For 1990-2009 cars

### Circuit Description

The provision for communicating with the Brake Pressure Modulator Valve (BPMV) is the data link connector (DLC). The DLC is located under the instrument panel. The DLC is used to link a scan tool to the BPMV serial data stream. Some common uses of the scan tool are listed below:

• | Identifying the stored diagnostic trouble codes (DTCs)

• | Reading the serial data stream

• | Clearing the DTCs

• | Storing the Freeze Frame data

### Diagnostic Aids

Some scan tools may require an external power supply. Make sure your scan tool is using the correct power feed.

Ensure that the correct application (model year, carline, VIN code) has been selected on the scan tool. If communications are still not established, try the scan tool on another vehicle in order to ensure that the scan tool or the connecting cables are not the cause of the malfunction. Always try the scan tool on a vehicle that uses the same DLC terminal for serial data communication.

Any circuitry that is suspect to an intermittent complaint should be thoroughly inspected for the following:

• | Backed-out terminals

• | Improper mating of terminals

• | Broken electrical connector locks

• | Improperly formed or damaged terminals

• | Faulty terminal-to-wiring connections

• | Physical damage to the wiring harness

• | A broken conductor inside the wire insulation

• | Corrosion of the electrical connections, the splices, or the terminals

### Test Description

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

1. This step checks whether the scan tool can communicate with other control modules on the vehicle. If the scan tool can communicate with the PCM then the DLC ground circuit (terminal 4) and the DLC ignition positive voltage circuit (terminal 16) are OK.

2. This step checks for an open BPMV-to-splice pack serial data circuit or for a defective BPMV.

3. This step checks for an open/shorted to ground circuit, a shorted to battery positive circuit, or for a defective scan tool.

4. The modules supply a low current (about 1.85 mA) voltage on the serial data circuit. The normal circuit low current will NOT illuminate a test lamp. If the circuit is shorted to battery positive the higher current will illuminate the test lamp.

5. The scan tool may be damaged by high current flow on the serial data circuit at DLC terminal 7. Verify the scan tool for proper operation on a known good vehicle that uses terminal 7 of the DLC for serial data communication.

Step | Action | Value | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Diagnostic System Check - Engine Controls ? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls in Engine Controls
2 |

1. Turn ON the ignition, with the engine OFF.
2. Attempt to establish communication with the BPMV.

Does the scan tool display the BPMV data?

--

System OK

Go to Step 3

3 | Is the vehicle equipped with ABS? | -- | Go to Step 4 | Go to Step 5
4 | Attempt to establish communication with the PCM. Does the scan tool display the PCM data? | -- | Go to Step 5 | Go to Step 6
5 |

1. Turn OFF the ignition.
2. Disconnect BPMV electrical connector cavity 4.
3. Test for an open serial data circuit between the BPMV and the splice pack SP255.
4. Repair as necessary.

Was a repair necessary?

--

Go to Step 2

Go to Step 12

6 |

1. Disconnect the scan tool.
2. Measure the voltage from the DLC connector terminal 7 to ground, using a DMM.

Is the voltage more than or equal to the specified value?

11 V

Go to Step 7

Go to Step 8

7 | Connect a test lamp between the DLC connector terminal 7 and ground. Does the test lamp illuminate? | -- | Go to Step 10 | Go to Step 11
8 |

1. Test for an open in the serial data circuit. The most likely location for an open serial data circuit is between the DLC connector terminal 7 and the splice pack SP255.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 2

Go to Step 9

9 |

1. Locate the short to ground in the serial data circuit.
2. Disconnect each circuit at the splice pack one at a time in order to determine which module or serial data circuit is shorted.
3. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 2

--

10 | Repair the short to battery positive voltage in the serial data circuit. Refer to Wiring Repairs in Wiring Systems. Scan tool damage may have occurred. Is the action complete? | -- | Go to Step 2 | --
11 | Replace the defective scan tool. Is the action complete? | -- | Go to Step 2 | --
12 | Inspect for poor connections at the harness connector of the BPMV. 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 2 | Go to Step 13
13 | Replace the BPMV. Refer to Brake Pressure Modulator Valve Assembly Replacement in Antilock Brake System. Is the action complete? | -- | Go to Step 2 | --