Test Description
WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The numbers below refer to the step numbers on the diagnostic table
- 2 . IF the engine does not start and the system sets DTC U1800, the fault lies in the FICM or the FICM power and ground circuits
- 3 . If the fault is a short to ground, a short together, or an open between the ECM and the CAN circuit splices, DTC U2104 will also set. These failures effect the entire system.
- 4 . If only DTC U1800 and U2106 set, The problem is a short to voltage in the SAE J1939 Serial Data Bus+ circuit. This failure does not set DTC U2104
DTC U1800
| Step | Action | Values | Yes | No |
|---|---|---|---|---|
| Schematic Reference: See appropriate Engine Controls schematic in SYSTEM WIRING DIAGRAMS | ||||
| 1 | Did you perform the Diagnostic System Check-Engine Controls? | - | Go to Step 2 | Go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS |
| 2 | Important: If DTC U1800 was set during a FRP relay output test with a scan tool, clear the DTC and do not follow this test. Attempt to start the engine. Does the engine start? |
- | Go to Step 3 | Go to Step 6 |
| 3 | Did DTC U2104 also set | - | Go to DTC U2104 | Go to Step 4 |
| 4 | Did only DTC U1800 and U2106 set? | - | Go to Step 10 | Go to Step 5 |
| 5 | 1. Observe the Freeze Frame/Failure Records for this DTC. 2. Turn OFF the ignition for 30 seconds. 3. Start the engine. 4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition? |
- | Go to Step 8 | Go to TESTING FOR INTERMITTENT AND POOR CONNECTIONS |
| 6 | Inspect the fuse supplying power to the FICM ignition 1 voltage circuits. Is the fuse open? |
- | Go to Step 15 | Go to Step 7 |
| 7 | 1. Turn ON the ignition with the engine OFF. 2. Probe the fuse supplying power to the FICM with a test lamp connected the a good ground. Does the test lamp illuminate? |
- | Go to Step 13 | Go to IGNITION RELAY Diagnosis |
| 8 | 1. Turn OFF the ignition. 2. Disconnect the ECM and FICM harness connectors. 3. Test the SAE J1939 Serial Data Bus+ circuit for an open between the CAN harness splice and the FICM. Did the resistance measure less than the specified value? |
5 | Go to Step 9 | Go to Step 17 |
| 9 | Test the SAE J1939 Serial Data Bus- circuit for an open between the CAN harness splice and the FICM. Did the resistance measure less than the specified value? |
5 | Go to Step 16 | Go to Step 18 |
| 10 | 1. Disconnect the ECM, FICM, and TCM if equipped. 2. Turn ON the ignition, with the engine OFF. 3. Probe the SAE J1939 Serial Data Bus+ circuit at the ECM harness connector with a test lamp connected to a good ground. Does the test lamp illuminate? |
- | Go to Step 19 | Go to Step 11 |
| 11 | 1. Turn OFF the ignition. 2. Reconnect the FICM harness connector. 3. Turn ON the ignition, with the engine OFF. 4. Probe the SAE J1939 Serial Data Bus+ circuit at the ECM harness connector with a test lamp connected to a good ground. Does the test lamp illuminate? |
- | Go to Step 20 | Go to Step 12 |
| 12 | Important: If the vehicle does not have an automatic transmission, answer this step NO. 1. Turn OFF the ignition. 2. Reconnect the TCM harness connector. 3. Turn ON the ignition, with the engine OFF. 4. Probe the SAE J1939 Serial Data Bus+ circuit at the ECM harness connector with a test lamp connected to a good ground. Does the test lamp illuminate? |
- | Go to Step 21 | Go to Step 22 |
| 13 | Test the FICM ignition 1 voltage circuits between the fuse and the FICM for an open, and test the entire FICM ignition 1 voltage circuit for high resistance and repair as necessary. Did you find and correct the condition |
- | Go to Step 23 | Go to Step 14 |
| 14 | Test the FICM ground circuits for an open or high resistance and repair as necessary. Did you find and correct the condition? |
- | Go to Step 23 | Go to Step 16 |
| 15 | 1. Disconnect the FICM. 2. Test the FICM ignition 1 voltage circuits for a short to ground and repair as necessary. Did you find and correct the condition? |
- | Go to Step 23 | Go to Step 20 |
| 16 | Test for an intermittent or poor connections at the FICM. Repair as necessary. Refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS
. Did you find and correct the condition? |
- | Go to Step 23 | Go to Step 20 |
| 17 | Repair the open or high resistance in the SAE J1939 Serial Data Bus+ circuit between the FICM and the CAN splice. Did you complete the repair? |
- | Go to Step 23 | - |
| 18 | Repair the open or high resistance in the SAE J1939 Serial Data Bus- circuit between the FICM and the CAN circuit splice. Did you complete the repair? |
- | Go to Step 23 | - |
| 19 | Repair the short to voltage in the SAE J1939 Serial Data Bus+ circuit. Did you complete the repair? |
- | Go to Step 23 | - |
| 20 | Replace the FICM. Refer to FUEL INJECTION CONTROL MODULE
Replacement. Did you complete the replacement? |
- | Go to Step 23 | - |
| 21 | Replace the TCM. Refer to TRANSMISSION CONTROL MODULE
Allison. Did you complete the replacement? |
- | Go to Step 23 | - |
| 22 | Replace the ECM. Refer to ENGINE CONTROL MODULE
Replacement. Did you complete the replacement? |
- | Go to Step 23 | - |
| 23 | 1. Clear the DTCs with a scan tool. 2. Turn OFF the ignition for 30 seconds. 3. Start the engine. 4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? |
- | Go to Step 1 | Go to Step 24 |
| 24 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? |
- | Go to DTC INDEX | System OK |