GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 1999 🢒 Grand Prix 🢒 Body and Accessories 🢒 Data Link Communications 🢒 Scan Tool Does Not Communicate with UART Data Line

Step

Action

Value(s)

Yes

No

1

Using a DMM, measure the voltage between the Data Link Connector (DLC) terminal 16 and ground.

Is the voltage within the specified range?

B+ (9-14 V)

Go to Step 2

Go to Step 15

2

Using a DMM, measure the voltage between B+ and DLC terminal 5.

Is the voltage within the specified range?

B+ (9-14 V)

Go to Step 3

Go to Step 16

3

Using a DMM, measure the voltage between B+ and DLC terminal 4.

Is the voltage within the specified range?

B+ (9-14 V)

Go to Step 4

Go to Step 16

4

Inspect for proper connection of the scan tool to the DLC.

Is the connection OK between the scan tool and the DLC?

--

Go to Step 5

Go to Step 17

5

Attempt to establish communication with the PCM on a different vehicle using the scan tool.

Can communication be established with the scan tool?

--

Go to Step 6

Go to Step 18

6
  1. Reconnect the scan tool to the DLC.
  2. Turn the ignition switch to the RUN position.
  3. Using a scan tool, re-attempt to establish communication with the Powertrain Control Module (PCM).

Can the scan tool communicate with the PCM?

--

Go to Step 19

Go to Step 7

7
  1. Turn the ignition switch OFF.
  2. Disconnect the PCM connector C1.
  3. Disconnect the EBTCM electrical connector (if equipped with ABS).
  4. Disconnect the trip calculator electrical connector (if equipped).
  5. Disconnect the heater-A/C control electrical connector C1 (if equipped with auto A/C).
  6. Using a DMM, measure the resistance between the DLC terminal 9 and the DLC terminal 5.

Is the resistance the same as the specified value?

OL (Infinite)

Go to Step 8

Go to Step 20

8
  1. Turn the ignition to the RUN position.
  2. Using a DMM, measure the voltage between the DLC terminal 9 and the DLC terminal 5.

Is the voltage less than the specified value?

1 V

Go to Step 9

Go to Step 21

9
  1. Turn the ignition to the OFF position.
  2. Using a DMM, measure the resistance between the DLC terminal 9 and the PCM harness connector C1 terminal 15.

Is the resistance within the specified value?

0-2 ohms

Go to Step 10

Go to Step 22

10
  1. If the vehicle is not equipped with ABS, go to Step 11 .
  2. Using a DMM, measure the resistance between the DLC terminal 9 and the EBTCM harness connector C1 terminal 24.

Is the resistance within the specified value?

0-2 ohms

Go to Step 11

Go to Step 22

11
  1. If the vehicle is not equipped with auto A/C, go to Step 12 .
  2. Using a DMM, measure the resistance between the DLC terminal 9 and the heater-A/C control harness connector terminal D12.

Is the resistance within the specified value?

0-2 ohms

Go to Step 12

Go to Step 22

12
  1. If the vehicle is not equipped with the trip calculator, go to Step 13 .
  2. Using a DMM, measure the resistance between the DLC terminal 9 and the trip calculator harness connector terminal A7.

Is the resistance within the specified value?

0-2 ohms

Go to Step 13

Go to Step 22

13
  1. Turn the ignition switch OFF.
  2. Reconnect the PCM only. Leave the other modules disconnected.
  3. Turn the ignition switch to the RUN position.
  4. Use a scan tool in order to establish communication with the PCM.

Can the scan tool communicate with the PCM?

--

Go to Step 14

Go to Step 23

14
  1. Turn the ignition switch OFF.
  2. Reconnect one of the disconnected modules.
  3. Turn the ignition switch to the RUN position.
  4. Use a scan tool in order to establish communication with the PCM.
  5. Repeat Steps 1-4 in this action step until the malfunctioning module is isolated.

Inspect for power, ground and proper connections to the module that is not communicating with the scan tool. Refer to the following sections for service procedures:

    • For the EBTCM, refer to Antilock Brake System in Brakes.
    • For the heater-A/C control, refer to Air Conditioning.
    • For the trip calculator, refer to Driver Information System Schematics.

Is the repair complete?

--

Go to Step 24

--

15

Repair the poor connection or an open in circuit 440.

Is the repair complete?

--

Go to Step 24

--

16

Repair the poor connection or an open in circuit 1550.

Is the repair complete?

--

Go to Step 24

--

17

Repair the poor connection between the DLC terminal 9 and the scan tool.

Is the repair complete?

--

Go to Step 24

--

18

The scan tool may be malfunctioning. Refer to the scan tool instruction manual for additional information.

Is the action complete?

--

Go to Step 24

--

19

The malfunction is intermittent and is not present at this time.

Inspect the connectors of the following components for a poor connection or open, a short to B+, or a short to ground in circuit 800:

    • The PCM
    • The EBTCM (if equipped)
    • The heater-A/C control module (if equipped)
    • The trip calculator (if equipped)

Is the repair complete?

--

Go to Step 24

--

20

Repair the short to ground in circuit 800.

Is the repair complete?

--

Go to Step 24

--

21
  1. Turn the ignition OFF.
  2. Repair the short to B+ in circuit 800.

Is the repair complete?

--

Go to Step 24

--

22

Repair the poor connection or an open in circuit 800.

Is the repair complete?

--

Go to Step 24

--

23

Check for power, ground and proper connections to the PCM. Refer to Engine Controls for additional information.

Is the action complete?

--

Go to Step 24

--

24
  1. Ensure that the ignition switch is OFF.
  2. Reconnect the connectors. Reinstall the components.

Is the action complete?

--

Go to Data Link Communications System Check

--