ISB/ISBe Series Engines – FAULT CODE 434

  Printable Version

Overview

Unswitched Battery Supply Circuit SMALL | MEDIUM | LARGE

Circuit Description

The electronic control module (ECM) receives constant voltage from the batteries through the unswitched battery wires that are connected directly to the positive (+) battery post. There is either one in-line 30-amp fuse or two in-line 15-amp fuses in the unswitched battery wires to protect the OEM harness from overheating. The ECM receives switched battery input through the vehicle keyswitch wire when the vehicle keyswitch is turned ON. The battery return wires are connected directly to the negative (-) battery post.

Component Location

The ECM is connected to the battery by the OEM harness. This direct link provides a constant power supply for the ECM. The location of the battery will vary with the OEM. Use the OEM manual.

Shop Talk

• If the ECM unswitched battery supply is taken from the starter, check for low voltage during cranking. Low voltage during cranking can cause the ECM power supply to drop below specifications and log Fault Code 434.
• Inspect the intermittent keyswitch or fast keyswitch cycling.

Note: If a battery disconnect switch is turned off after the keyswitch is turned off, but before the ECM completely powers down (up to 20 seconds), this fault can register.

Verify that the ECM unswitched power is coming from the batteries and not the starter or other device. Check for low voltage during cranking. Low voltage during cranking can cause the ECM power supply to drop below specifications and log Fault Code 434.

Corrupted voltage (short interruptions or spikes that can only be seen with a with a oscilloscope) on keyswitch line can cause this fault. If the voltage at pin 5 of the engine 36-pin connector is measured as negative with a oscilloscope at key-off, Fault Code 434 can be logged.

Refer to Troubleshooting Fault Code t05-434