For 1990-2009 cars

## Scan Tool Does Not Communicate with Vehicle Control Module/Powertrain Control Module 1.6L

### Circuit Description

The provision for communicating with the powertrain control module (PCM) 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 PCM 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 that your scan tool is using the correct power feed.

Check that the correct application - model year, car line, 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.

An intermittent malfunction may be caused by a fault in the serial data circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions in Engine Controls.

### Test Description

The numbers below refer to the step numbers in 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 one of the other modules then the DLC connector, the shared circuits, and the scan tool are OK.

2. 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.

3. If the engine starts and runs, the main relay is OK.

4. This step checks whether the PCM is receiving ignition positive voltage from the IG fuse located in the Junction Block. The main relay will not energize and the PCM can not provide serial data without ignition positive voltage from the IG fuse circuit.

5. This step checks whether the PCM is receiving ignition positive voltage from the main relay when the ignition is ON. The PCM can not provide serial data without ignition positive voltage from the main relay.

6. The PCM can not provide serial data without the correct power and grounds.

7. The scan tool may be damaged by high current flow on the serial data circuit at DLC terminal 7. Check 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
--- | --- | --- | --- | ---
Schematic Reference: Data Link Connector Schematics and Engine Controls Schematics in Engine Controls -- 1.6L
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, leaving the engine OFF.
2. Attempt to establish communication with the PCM.

Does the scan tool display the PCM data?

--

System OK

Go to Step 3

3 | Attempt to establish communication with the Inflatable Restraint Sensing and Diagnostic Module (SDM). Does the scan tool display communicate with the SDM? | -- | Go to Step 6 | Go to Step 4
4 |

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

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

9.0 V

Go to Step 5

Go to Step 11

5 | Connect a test lamp between the DLC connector terminal 7 and ground. Does the test lamp illuminate? | -- | Go to Step 14 | Go to Step 15
6 |

1. Turn OFF the ignition.
2. Disconnect the PCM electrical connector containing the serial data circuit.
3. Turn ON the ignition, leaving the engine OFF.
4. Measure the voltage of the serial data circuit, on the harness side, with a DMM.

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

9.0 V

Go to Step 7

Go to Step 13

7 | Start the engine. Does the engine start and run? | -- | Go to Step 19 | Go to Step 8
8 | Check for system voltage at PCM terminal C2-20 from the IG fuse in the Junction Block. Is the voltage more than or equal to the specified value? | 11 V | Go to Step 9 | Go to Step 16
9 |

1. Turn OFF the ignition.
2. Connect the PCM electrical connector.
3. Turn ON the ignition, leaving the engine OFF.
4. Use a DMM to check for system voltage to PCM terminals C2-4 and C2-15 from the main relay.

Is the voltage more than or equal to the specified value on both circuits supplying system voltage from the main relay?

11 V

Go to Step 10

Go to Step 18

10 |

1. Turn OFF the ignition.
2. Disconnect the PCM electrical connectors.
3. Probe the PCM ground circuits, harness side, with a test lamp connected to B+.

Did the test lamp illuminate for all 5 PCM ground circuits?

--

Go to Step 19

Go to Step 17

11 |

1. Check for an open in the serial data circuit between the DLC connector terminal 7 and the splice pack S260.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 2

Go to Step 12

12 |

1. Locate the short to ground in the serial data circuit.
2. Disconnect each circuit at the splice, 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.

Did you complete the repair?

--

Go to Step 2

--

13 | Repair the open in the serial data circuit between the PCM and the splice S260. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 2 | --
14 | 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. Did you complete the repair? | -- | Go to Step 2 | --
15 |

1. Check that all of the following scan tool selections are correct:

• | Model year

• | Car line or Truck line

• | Engine option (VIN)

• | Transmission option

2. If all the selections are correct and the scan tool does not display any engine data, replace the defective scan tool.

Did you complete the repair?

--

Go to Step 2

--

16 | Repair the fault in the ignition positive voltage circuit from the IG fuse in the Junction Block. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 2 | --
17 | Repair the open in the PCM ground circuit as necessary. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 2 | --
18 |

1. Check for a fault in the ignition positive voltage circuit from the main relay to the PCM.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 2

Go to Ignition Relay Diagnosis in Engine Controls

19 |

1. Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections .
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 2

Go to Step 20

20 | Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls. Is the replacement complete? | -- | Go to Step 2 | --

## Scan Tool Does Not Communicate with Vehicle Control Module/Powertrain Control Module 2.0L

### Circuit Description

The provision for communicating with the powertrain control module (PCM) 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 PCM 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 that your scan tool is using the correct power feed.

Check that the correct application - model year, car line, 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.

An intermittent malfunction may be caused by a fault in the serial data circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions in Engine Controls.

### Test Description

The numbers below refer to the step numbers in 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 one of the other modules then the DLC connector, the shared circuits, and the scan tool are OK.

2. 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.

3. If the engine starts and runs, the main relay is OK.

4. This step checks whether the PCM is receiving ignition positive voltage from the IG fuse located in the Junction Block. The main relay will not energize and the PCM can not provide serial data without ignition positive voltage from the IG fuse circuit.

5. This step checks whether the PCM is receiving ignition positive voltage from the main relay when the ignition is ON. The PCM can not provide serial data without ignition positive voltage from the main relay.

6. The PCM can not provide serial data without the correct power and grounds.

7. The scan tool may be damaged by high current flow on the serial data circuit at DLC terminal 7. Check 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
--- | --- | --- | --- | ---
Schematic Reference: Data Link Connector Schematics and Engine Controls Schematics in Engine Controls -- 2.0 L
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, leaving the engine OFF.
2. Attempt to establish communication with the PCM.

Does the scan tool display the PCM data?

--

System OK

Go to Step 3

3 | Attempt to establish communication with the Inflatable Restraint Sensing and Diagnostic Module (SDM). Does the scan tool display communicate with the SDM? | -- | Go to Step 6 | Go to Step 4
4 |

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

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

9.0 V

Go to Step 5

Go to Step 11

5 | Connect a test lamp between the DLC connector terminal 7 and ground. Does the test lamp illuminate? | -- | Go to Step 14 | Go to Step 15
6 |

1. Turn OFF the ignition.
2. Disconnect the PCM electrical connector containing the serial data circuit.
3. Turn ON the ignition, leaving the engine OFF.
4. Measure the voltage of the serial data circuit, on the harness side, with a DMM.

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

9.0 V

Go to Step 7

Go to Step 13

7 | Start the engine. Does the engine start and run? | -- | Go to Step 19 | Go to Step 8
8 | Check for system voltage at PCM terminal C2-20 from the IG fuse in the Junction Block. Is the voltage more than or equal to the specified value? | 11 V | Go to Step 9 | Go to Step 16
9 |

1. Turn OFF the ignition.
2. Connect the PCM electrical connector.
3. Turn ON the ignition, leaving the engine OFF.
4. Use a DMM to check for system voltage to the PCM terminals C2-4 and C2-15 from the main relay.

Is the voltage more than or equal to the specified value on both circuits supplying system voltage from the main relay?

11 V

Go to Step 10

Go to Step 18

10 |

1. Turn OFF the ignition.
2. Disconnect the PCM electrical connectors.
3. Probe the PCM ground circuits, harness side, with a test lamp connected to B+.

Did the test lamp illuminate for all 5 PCM ground circuits?

--

Go to Step 19

Go to Step 17

11 |

1. Check for an open in the serial data circuit between the DLC connector terminal 7 and the splice pack S260.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 2

Go to Step 12

12 |

1. Locate the short to ground in the serial data circuit.
2. Disconnect each circuit at the splice, 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.

Did you complete the repair?

--

Go to Step 2

--

13 | Repair the open in the serial data circuit between the PCM and the splice S260. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 2 | --
14 | 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. Did you complete the repair? | -- | Go to Step 2 | --
15 |

1. Check that all of the following scan tool selections are correct:

• | Model year

• | Car line or Truck line

• | Engine option (VIN)

• | Transmission option

2. If all the selections are correct and the scan tool does not display any engine data, replace the defective scan tool.

Did you complete the repair?

--

Go to Step 2

--

16 | Repair the fault in the ignition positive voltage circuit from the IG fuse in the Junction Block. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 2 | --
17 | Repair the open in the PCM ground circuit as necessary. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 2 | --
18 |

1. Check for a fault in the ignition positive voltage circuit from the main relay to the PCM.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 2

Go to Ignition Relay Diagnosis in Engine Controls

19 |

1. Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 2

Go to Step 20

20 | Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls. Is the replacement complete? | -- | Go to Step 2 | --

## Scan Tool Does Not Communicate with Vehicle Control Module/Powertrain Control Module 2.5L

### Circuit Description

The provision for communicating with the powertrain control module (PCM) 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 PCM 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 that your scan tool is using the correct power feed.

Check that the correct application - model year, car line, 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.

An intermittent malfunction may be caused by a fault in the serial data circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions in Engine Controls.

### Test Description

The numbers below refer to the step numbers in 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 one of the other modules then the DLC connector, the shared circuits, and the scan tool are OK.

2. 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.

3. If the engine starts and runs, the main relay is OK.

4. This step checks whether the PCM is receiving ignition positive voltage from the IG fuse located in the Junction Block. The main relay will not energize and the PCM can not provide serial data without ignition positive voltage from the IG fuse circuit.

5. This step checks whether the PCM is receiving ignition positive voltage from the main relay when the ignition is ON. The PCM can not provide serial data without ignition positive voltage from the main relay.

6. The PCM can not provide serial data without the correct power and grounds.

7. The scan tool may be damaged by high current flow on the serial data circuit at DLC terminal 7. Check 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
--- | --- | --- | --- | ---
Schematic Reference: Data Link Connector Schematics and Engine Controls Schematics in Engine Controls - 2.5L
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, leaving the engine OFF.
2. Attempt to establish communication with the PCM.

Does the scan tool display the PCM data?

--

System OK

Go to Step 3

3 | Attempt to establish communication with the Inflatable Restraint Sensing and Diagnostic Module (SDM). Does the scan tool display communicate with the SDM? | -- | Go to Step 6 | Go to Step 4
4 |

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

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

9.0 V

Go to Step 5

Go to Step 11

5 | Connect a test lamp between the DLC connector terminal 7 and ground. Does the test lamp illuminate? | -- | Go to Step 14 | Go to Step 15
6 |

1. Turn OFF the ignition.
2. Disconnect the PCM electrical connector containing the serial data circuit.
3. Turn ON the ignition, leaving the engine OFF.
4. Measure the voltage of the serial data circuit, on the harness side, with a DMM.

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

9.0 V

Go to Step 7

Go to Step 13

7 | Start the engine. Does the engine start and run? | -- | Go to Step 19 | Go to Step 8
8 | Check for system voltage at PCM terminal C4-3 from the IG fuse in the Junction Block. Is the voltage more than or equal to the specified value? | 11 V | Go to Step 9 | Go to Step 16
9 |

1. Turn OFF the ignition.
2. Connect the PCM electrical connector.
3. Turn ON the ignition, leaving the engine OFF.
4. Use a DMM to check for system voltage to PCM terminals C4-20 and C4-21 from the main relay.

Is the voltage more than or equal to the specified value on both circuits supplying system voltage from the main relay?

11 V

Go to Step 10

Go to Step 18

10 |

1. Turn OFF the ignition.
2. Disconnect the PCM electrical connectors.
3. Probe the PCM ground circuits, harness side, with a test lamp connected to B+.

Did the test lamp illuminate for all 5 PCM ground circuits?

--

Go to Step 19

Go to Step 17

11 |

1. Check for an open in the serial data circuit between the DLC connector terminal 7 and the splice pack S260.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 2

Go to Step 12

12 |

1. Locate the short to ground in the serial data circuit.
2. Disconnect each circuit at the splice, 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.

Did you complete the repair?

--

Go to Step 2

--

13 | Repair the open in the serial data circuit between the PCM and the splice S260. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 2 | --
14 | 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. Did you complete the repair? | -- | Go to Step 2 | --
15 |

1. Check that all of the following scan tool selections are correct:

• | Model year

• | Car line or Truck line

• | Engine option (VIN)

• | Transmission option

2. If all the selections are correct and the scan tool does not display any engine data, replace the defective scan tool.

Did you complete the repair?

--

Go to Step 2

--

16 | Repair the fault in the ignition positive voltage circuit from the IG fuse in the Junction Block. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 2 | --
17 | Repair the open in the PCM ground circuit as necessary. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 2 | --
18 |

1. Check for a fault in the ignition positive voltage circuit from the main relay to the PCM.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 2

Go to Ignition Relay Diagnosis in Engine Controls

19 |

1. Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 2

Go to Step 20

20 | Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls. Is the replacement complete? | -- | Go to Step 2 | --