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For 1990-2009 cars only
Makes 🢒 Geo 🢒 1996 🢒 Tracker - 4WD 🢒 Engine 🢒 Engine Controls - 1.6L 🢒 Data Link Connector Diagnosis

Schematic Reference: Engine Controls Schematics

Circuit Description

The provision for communicating with the engine control module (ECM) is the data link connector (DLC). It is usually located under the instrument panel. The DLC is used to connect to a scan tool. Some common uses of the scan tool are listed below:

    • Identifying stored Diagnostic Trouble Codes (DTCs).
    • Clearing stored DTCs.
    • Storing freeze frame data.
    • Reading serial data.

Diagnostic Aids

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

Check that the correct application (model year, carline, VIN code) has been selected on the scan tool. If communications still can not be established, try the scan tool on another vehicle to ensure that the scan tool or cables are not the cause of the malfunction.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

Any circuitry, that is suspected as causing an intermittent complaint, should be thoroughly checked 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.
    • Corrosion of electrical connections, splices, or terminals.

Test Description

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

  1. The Powertrain (OBD) System Check prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

    2.

  2. This step checks to see if the scan tool can establish communications.

    3.

  3. This step checks for B+ at the DLC battery positive voltage terminal.

    4.

  4. This step checks for B+ at the DLC serial data terminal.

    5.

  5. This step checks the ground circuits at the DLC.

    6.

  6. This step checks for voltage in the ignition positive circuit. If voltage is present at the ECM the malfunction is most likely a faulty main relay or faults in the relay circuitry.

Step

Action

Value(s)

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 ON the ignition, leaving the engine OFF.
  2. Install a scan tool.

Does the scan tool display engine data?

--

Go to Diagnostic Aids

Go to Step 3

3
  1. Check the following fuses for an open condition.
    2. • FI fuse
    • IG-COIL METER fuse
    • TAIL DOME fuse
  2. Repair as necessary.

Was a repair necessary?

--

Go to Step 21

Go to Step 4

4

  1. Turn ON the ignition, leaving the engine OFF.
  2. Measure the voltage from terminal 16 of the DLC to ground with a DMM.

Is the voltage near the specified value?

B+

Go to Step 5

Go to Step 7

5

Measure the voltage from terminal 7 of the DLC to ground, with a DMM.

Is the voltage near the specified value?

B+

Go to Step 6

Go to Step 8

6

Probe the DLC terminals 4 and 5 (ground circuit terminals), using a test lamp connected to battery positive voltage.

Does the test lamp illuminate for both circuits?

--

Go to Step 20

Go to Step 9

7

Repair the open or short in the battery circuit between the Fuse Block 2 and the DLC.

Is the action complete?

--

Go to Step 21

--

8
  1. Check for an open or a short in the serial data circuit between the ECM and the DLC.
  2. Repair as necessary.

Was a repair necessary?

--

Go to Step 21

Go to Step 10

9

Repair the open in the DLC ground circuit.

Is the action complete?

--

Go to Step 21

--

10

  1. Turn the ignition ON, leaving the engine OFF.
  2. Backprobe the ECM ignition positive voltage terminals, using a test lamp connected to ground.

Does the test lamp illuminate at both terminals?

--

Go to Step 19

Go to Step 11

11
  1. Check for an open or a short in the ignition positive voltage circuit between the ECM and the main relay.
  2. Repair as necessary.

Was a repair necessary?

--

Go to Step 21

Go to Step 12

12
  1. Turn OFF the ignition.
  2. Disconnect the main relay.
  3. Turn ON the ignition, leaving the engine OFF.
  4. Probe terminal 2 (harness side), using a test lamp connected to ground.

Does the test lamp illuminate?

--

Go to Step 13

Go to Step 15

13

Probe terminal 1 of the main relay (harness side), using a test lamp connected to ground.

Does the test lamp illuminate?

--

Go to Step 14

Go to Step 16

14
  1. Turn OFF the ignition.
  2. Probe terminal 3 of the main relay, using a test lamp connected to battery positive voltage.
  3. Turn ON the ignition, leaving the engine OFF.
  4. Observe the test lamp.

Does the test lamp illuminate?

--

Go to Step 18

Go to Step 17

15

Repair the open or a short to ground in the power feed circuit between the main relay and the FI fuse.

Is the action complete?

--

Go to Step 21

--

16

Repair the open or the short in the ignition feed circuit between the main relay and the IG-COIL METER fuse.

Is the action complete?

--

Go to Step 21

--

17
  1. Check for an open in the main relay control circuit between the main relay and the ECM.
  2. Repair as necessary.

Was a repair necessary?

--

Go to Step 21

Go to Step 19

18

Replace the main relay.

Is the action complete?

--

Go to Step 21

--

19

Replace the ECM. Refer to Engine Control Module Replacement.

Is the action complete.

--

Go to Step 21

--

20

The scan tool is faulty. Refer to the scan tool manual for repair information.

Is the action complete?

--

Go to Step 21

--

21

Turn ON the ignition, leaving the engine OFF.

Does the scan tool display engine data?

--

System OK

Go to Diagnostic Aids