Data Link Connector Diagnosis. Geo Prizm 1997

For 1990-2009 cars

Schematic Reference: Engine Controls Schematics .

### 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

• | Performing output control tests

### 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 locks

• | Improperly formed or damaged terminals

• | Physical damage to the wiring harness

• | Poor terminal to wiring connections

• | Corrosion

### Test Description

The numbers below refer to the step numbers in the Diagnostic Table.

1. If the scan tool requires an external power supply, check the external supply for proper voltage and ground as well as the voltage and ground supplies in the DLC.

2. Unlike the UART serial data circuit, the only time any of the Class 2 serial data circuit has any voltage on it is when a scan tool asks the PCM for information and the PCM sends the information out.

3. If the no voltage condition was due to a blown fuse, locate and repair any shorts that may have caused the fuse to blow before replacement.

4. If the scan tool will not display scan data, refer to Diagnostic Aids. If the scan tool can communicate with the PCM and you were sent here from the OBD System Check table, return to that table and complete the diagnostics there.

5. The scan tool, VIM or associated cables could be faulty. Refer to the scan tools manual for repair information.

Step | Action | Value | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check

2

1. Turn the ignition switch ON, with the engine OFF.
2. Install a scan tool.

Does the scan tool power up?

--

Go to Step 3

Go to Step 4

3

1. Disconnect the scan tool.
2. With a test light connected to ground, probe the Class 2 serial data terminal 2 at the DLC.

Does the test light remain OFF?

--

Go to Step 5

Go to Step 6

4 | With the test light connected to ground, probe the DLC battery feed circuit terminal 16. Does the test light illuminate? | -- | Go to Step 7 | Go to Step 8
5 | With a test light connected to B+, probe the Class 2 serial data terminal 2 at the DLC. Does the test light remain OFF? | -- | Go to Step 9 | Go to Step 10
6 | Check the Class 2 serial data circuit for a short to voltage and repair as necessary. Was a repair necessary? | -- | Go to Step 16 | Go to Step 11
7 | With the test light connected to B+, probe the specified DLC ground circuit terminals 4 and 5. Does the test light illuminate for both circuits? | 11 volts | Go to Step 15 | Go to Step 12

8

1. Check the OBD II Fuse for an open.
2. If OK, repair the open or short to ground in the DLC battery feed circuit.

Is the action complete?

--

Go to Step 16

--

9 | Check the Class 2 serial data circuit for an open and repair if necessary. Was a repair necessary? | -- | Go to Step 16 | Go to Step 13
10 | Check the Class 2 serial data circuit for a short to ground and repair as necessary. Was a repair necessary? | -- | Go to Step 16 | Go to Step 11
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 16 | --
12 | Repair the open in the DLC ground circuits. Is the action complete? | -- | Go to Step 16 | --
| Reinstall the scan tool. Can the scan tool communicate with the PCM? | -- | Go to Step 16 | Go to Step 14
14 | Install the scan tool on a another vehicle and check for proper operation. Does the scan tool work properly on a different vehicle? | -- | Go to Step 11 | Go to Step 15
15 | The scan tool is faulty. Refer to the scan tools manual for repair information. Is the action complete? | -- | Go to Step 16 | --

16

1. Using a scan tool, clear the DTCs.
2. Attempt to start the engine.

Does the engine start and continue to run?

--

Go to Step 17

Go to Step 1

17

1. Allow the engine to idle until normal operating temperature is reached.
2. Check if any DTCs are set.

Are any DTCs displayed that have not been diagnosed?

--

Go to the applicable DTC table

System OK