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Electronic Control System Gas Plus Engines – FAULT CODE 343

ECM – Warning Internal Hardware Failure

Overview

CODE REASON EFFECT
Fault Code: 343
PID: 254
SPN: 629
FMI: 12
LAMP: Yellow
SRT: 

Internal ECM error.

Engine possibly will not start or run.

ECM
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Circuit Description

The electronic control module (ECM) is a computer that is responsible for engine control, diagnostics, and user features.

Component Location

The ECM is located on the side of the engine, next to the ignition control module (ICM).

Shop Talk

This fault code can only be caused by an internal ECM problem. Repairs to the ECM are not possible.

Cautions and Warnings

 CAUTION 

To reduce the possibility of damaging a new ECM, all other active fault codes must be investigated prior to replacing the ECM.

Troubleshooting Steps

STEPS SPECIFICATIONS
STEP 1. Check the ECM.  
  STEP 1A. Check for fault codes. Fault Code 343 active?
  STEP 1B. Check the power supply. Constant +12 VDC power supply to the ECM?
  STEP 1C. Check ECM for a short circuit to ground. More than 100k ohms?
  STEP 1D. Recalibrate the ECM. ECM recalibrated successfully?
STEP 2. Clear the fault codes.  
  STEP 2A. Disable the fault code. Fault Code 343 inactive?
  STEP 2B. Clear the inactive fault codes. All fault codes cleared?

Guided Step 1 – Check the ECM.

Guided Step 1A – Check for fault codes.

Conditions

  • Turn keyswitch ON
  • Connect the INSITE™ electronic service tool.

Action

  • Recycle the power to the ECM using the keyswitch.

Fault Code 343 active?
YES NO
No Repair No Repair

Guided Step 1B – Check the power supply.

Conditions

  • Turn keyswitch ON.

Action

  • Inspect the power supply to the ECM.
  • Check the OEM connector as a possible source of an intermittent power supply.

Constant +12 VDC power supply to the ECM?
YES NO
No Repair

Intermittent power supply to the 31-pin OEM connector. Refer to the OEM service manual.

Guided Step 1C – Check ECM for a short circuit to ground.

Conditions

  • Turn keyswitch OFF
  • Disconnect engine harness connector 1 and connector 2 from the ECM.

Action

  • Measure the resistance from engine block ground to all pins in the ECM connector ports.
  • Measure the resistance from battery (-) post to all pins in the ECM connector ports.

More than 100k ohms?
YES NO
No Repair

Replace the ECM.

Call for pre-authorization. Refer to Procedure 019-031.

Guided Step 1D – Recalibrate the ECM.

Conditions

  • Turn keyswitch OFF
  • Connect all components.

Action

ECM recalibrated successfully?
YES NO
No Repair

Active fault codes present.

Replace the ECM.

Call for pre-authorization. Refer to Procedure 019-031.

Guided Step 2 – Clear the fault codes.

Guided Step 2A – Disable the fault code.

Conditions

  • Connect all components
  • Turn keyswitch ON.

Action

  • Start the engine and let it idle for one minute.
  • Verify that Fault Code 343 is inactive.

Fault Code 343 inactive?
YES NO
No Repair

Troubleshooting procedures need to be repeated from the beginning.

Guided Step 2B – Clear the inactive fault codes.

Conditions

  • Connect all components
  • Turn keyswitch ON.

Action

  • Use INSITE™ electronic service tool to erase the inactive fault codes.

All fault codes cleared?
YES NO
No Repair

Troubleshoot any remaining active fault codes.
Repair complete
Appropriate troubleshooting charts
Last Modified:  03-Aug-2004
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Published by Jack

Hello, I'm Jack, a diesel engine fan and a blogger. I write about how to fix and improve diesel engines, from cars to trucks to generators. I also review the newest models and innovations in the diesel market. If you are interested in learning more about diesel engines, check out my blog and leave your feedback.