For 1990-2009 cars
Automatic Transmission Components
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice

### Circuit Description

The diagnostic tables in this section are, by design, for use with a scan tool. If the scan tool is inoperative, correct the scan tool before beginning any other diagnostic procedures. The DLC connector powers the scan tool, DLC terminal 16 provides the B+ power. DLC terminal 4 provides the ground for the scan tool's power supply. DLC terminal 5 is an additional ground for serial data. Serial data for Powertrain diagnostics is on DLC terminal 7.

### Test Description

The number(s) below refer to the step number(s) on the Diagnostic Table.

1. If the ground circuit on DLC terminal 4 opens after the Scan Tool is up and running, the screen will go blank but the Scan Tool may remain on. If there is no ground at terminal 4 initially, the Scan Tool will not power up.

2. Some of the older Scan Tool receive power through a separate power cord from the cigar lighter. If you use this type of Scan Tool ,and the tool will not power up, check the cigar lighter socket for damage or a poor connection. Refer to Cigar Lighter/Auxiliary Outlets System Check in Wiring Systems for circuit details.

3. If there is no communication between the TCM and the Scan Tool , no data will be displayed. Serial Data is disrupted when the system voltage is below 9.0 Volts or above 16.0 Volts. A Scan Tool will not display the data if the system voltage is outside of this range. If no data is displayed with the engine running, but the data is displayed with the ignition ON, engine OFF, high system voltage (overcharging) may be at fault. If this is the case, the Scan Tool should display DTC P0560 System Voltage with the ignition ON and the engine OFF,

4. Try the Scan Tool on another Catera if one is available. The Catera uses ISO serial data and communicates with the Scan Tool on DLC terminal 7. Most other GM OBD II vehicles use Class 2 serial data on DLC terminal 2. Therefore, testing the Scan Tool on a vehicle that uses a different serial data system will not verify that the tool can communicate properly on terminal 7. An alternate approach is to try a different Scan Tool on the same vehicle if one is available. Before trying a different Scan Tool , check for a poor connection between the DLC and the Scan Tool cable.

   Refer to General Electrical Diagnosis in Wiring Systems.

5. Before trying a different Scan Tool , check for a poor connection between the DLC and the Scan Tool cable.

   Refer to General Electrical Diagnosis in Wiring Systems.

#### No Scan Tool Data

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to On-Board Diagnostic System Check
2 |

1. Connect the Scan Tool to the DLC connector.
2. With the engine OFF, turn the ignition switch to the RUN position.

Is the Scan Tool powered up?

--

Go to Step 3

Go to Step 9

3 | Does the engine start and run? | -- | Go to Step 12 | Go to Step 4
4 |

1. Turn the ignition switch to the OFF position.
2. Disconnect the TCM.
3. Use the J 35616-200 test light connected to battery ground in order to probe the ignition feed circuit in the TCM harness connector.

Does the test light illuminate?

--

Go to Step 5

Go to Step 6

5 | Use J 35616-200 connected to B+, in order to probe the TCM ground circuits in the TCM harness connector. Does the test light illuminate on all of the circuits? | -- | Go to Step 16 | Go to Step 7
6 | Repair the ignition feed circuit. Is the action complete? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
7 | Repair the open/high resistance in the affected circuit. Is the action complete? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
8 | Repair the short to ground in the affected circuit. Is the action complete? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
9 |

1. Disconnect the Scan Tool from the DLC.
2. Use J 35616-200 connected to chassis ground in order to probe DLC terminal 16.

Does the test light illuminate?

--

Go to Step 10

Go to Step 11

10 | Use J 35616-200 connected to B+ in order to probe DLC terminal 4 and terminal 5. Does the test light illuminate on both of the circuits? | -- | Go to Step 18 | Go to Step 14
11 | Repair the B+ circuit to DLC terminal 16. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
12 |

1. Disconnect the Scan Tool from the DLC.
2. Use the J 35616-200 connected to B+ in order to probe DLC terminal 4 and terminal 5.

Does the test light illuminate on both of the circuits?

--

Go to Step 13

Go to Step 14

13 | Check the Serial Data circuit to DLC Pin 7 for being open, shorted to power or ground. Refer to Wiring Repairs in Wiring Systems. Was a condition found and corrected? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | Go to Step 15
14 | Repair the open/high resistance ground circuit to DLC connector. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
15 | Verify the Scan Tool operation on another vehicle. Does the Scan Tool display data? | -- | Go to Step 16 | Go to Step 18
16 | Check the TCM harness connector for a poor connection or poor terminal tension. Refer to General Electrical Diagnosis in Wiring Systems. Was a condition found and corrected? | -- | Go to On-Board Diagnostic System Check | Go to Step 17
17 | Replace the TCM. Refer to Transmission Control Module Replacement . Is the action complete? | -- | Go to On-Board Diagnostic System Check | --
18 | Replace the malfunctioning Scan Tool . Is the action complete? | -- | Go to On-Board Diagnostic System Check | --