- Truck Engine:
- 3126B (S/N: 7AS)
Introduction
OEM harnesses may not contain flyback diodes that suppress transient voltage spikes. Problems that are related to the voltage spikes may occur in the ignition circuit of the ECM. If the ECM is damaged by these voltage spikes, the engine will not shut down. The accessories that are connected to the ignition key switch may also continue to operate after the key switch is turned to the OFF position. In order to eliminate this problem, the addition of the 161-7153 Harness Assembly to the OEM harness is required when you are replacing the ECM on a 3126B Truck Engine.
It is critical that the 161-7153 Harness Assembly is installed BEFORE you replace the ECM. Otherwise, the new ECM may also be damaged.
This entire Special Instruction should be read and understood before beginning any work on the engine.
Troubleshooting
Perform the following procedure in order to determine if the ECM has been damaged:
- Start the engine.
- Turn the ignition key switch to the OFF position. The engine should shut down. If the engine does not shut down, remove Terminal 70 from the ECM Vehicle Harness Connector P1. The engine should shut down. If the engine does not shut down, the ECM has been damaged. The ECM must be replaced.
Installation
 | |
| Illustration 1 | g00465674 |
161-7153 Harness Assembly | |
- Remove Terminal 70 from the ECM Vehicle Harness Connector P1. Insert Terminal 70 into the Deutsch in-line splice (1) of the 161-7153 Harness Assembly .
- Connect the red wire (2) of the 161-7153 Harness Assembly into Terminal 70 of the ECM Vehicle Harness Connector P1.
- Remove the sealing plug from the unused socket in Terminal 1 of the ECM Vehicle Harness Connector P1.
- Insert the black wire (3) of the 161-7153 Harness Assembly into Terminal 1 of the ECM Vehicle Harness Connector P1.
- Secure the 161-7153 Harness Assembly with a tie-wrap.
- Continue with the replacement procedure for the ECM.