FAULT CODE 343

Fault Processing Computer (FPC) Chip

Overview

CODE REASON EFFECT
Fault Code: 343
PID: S254
SPN: 629
FMI: 12
LAMP: Yellow
SRT: 00-606

Microprocessor communication error inside ECM.

None on performance.

Electronic Control Module

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Circuit Description

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

Component Location

The ECM is bolted to the left side of the engine.

Shop Talk

  • Loose engine or chassis ground connections can cause Fault Code 343 to be logged. Pay special attention to the negative starter post connection.
  • Complaints of an intermittent stumble are possible.
  • Moisture in the ECM connectors can also cause the ECM to log Fault Code 343.
  • A damaged engine position sensor can cause the ECM to log Fault Code 343 and possibly Fault Code 121 and Fault Code 115.
  • Defective alternators occasionally cause Fault Code 343. Run the engine with the alternator belt off; if the fault code becomes inactive, replace the alternator.
  • Intermittent battery shorts to ground can cause the fault.
  • Intermittent shorts to ground in these circuits can cause Fault Code 343: Injector solenoids, injector harnesses, fan clutch solenoids, fan clutch wiring, engine brake solenoids, engine brake wiring, OEM-installed engine speed sensors, flywheel housing and associated wiring, datalink wiring, and fuel shutoff solenoid or wiring.
  • Voltage on the keyswitch input to the ECM, when the key is in the OFF or ACCESSORY position, can cause Fault Code 343 due to the ECM ignoring a power-down request.
  • To determine if conducted electrical noise through the grounds is causing Fault Code 343, unbolt the ECM, and move it away from the engine block so that it is isolated from the engine block ground. If the fault is not duplicated, troubleshoot for the source of the electrical noise.

Cautions and Warnings


 CAUTION 

To reduce the possibility of pin and harness damage, use the following test leads when taking a measurement:
Part Number 3822758 – male Deutsch/AMP/Metri-Pack test lead
Part Number 3823995 – female AMP/Metri-Pack test lead.

 CAUTION 

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

 CAUTION 

To reduce the possibility of pin and harness damage, use the following test lead when taking a measurement:
Part Number 3822758 – male Deutsch/AMP/Metri-Pack test lead.

Troubleshooting Steps

STEPS SPECIFICATIONS
STEP 1. Check for active fault codes.  
  STEP 1A. Read the fault codes. Fault Code 343 active
STEP 2. Check the power and ground connections.  
  STEP 2A. Check all engine and chassis power and ground connections. Clean and tight
  STEP 2B. Check all power and ground resistances. Less than 10 ohms
  STEP 2C. Check battery grounds. Meets OEM specifications
STEP 3. Check for moisture in the ECM connectors.  
  STEP 3A. Check for moisture in the ECM connectors. All connectors dry
STEP 4. Check the engine position sensor (EPS).  
  STEP 4A. Check the engine position sensor for damage. No damage
  STEP 4B. Check the engine position sensor polarity. Correct polarity
  STEP 4C. Check for alternator-induced Fault Code 343. Fault Code 343 inactive
  STEP 4D. Check engine brake circuit. Fault Code 343 inactive
  STEP 4E. Check datalink wiring. Fault Code 343 inactive
  STEP 4F. Check OEM-installed components. Fault Code 343 inactive
  STEP 4G. Check injector circuits for intermittent shorts. Fault Code 343 inactive
  STEP 4H. Check fuel shutoff solenoid for shorts. Fault Code 343 inactive
  STEP 4I. Check fuel shutoff solenoid for open circuit. Fault Code 343 inactive
STEP 5. Clear the fault codes.  
  STEP 5A. Disable the fault code. Fault Code 343 inactive
  STEP 5B. Clear the inactive fault codes. All fault codes cleared


Guided Step 1 – Check for active fault codes.

Guided Step 1A – Read the fault codes.

Conditions

Turn keyswitch ON.

Action

  • Read the fault codes using INSITE™ electronic service tool.
OK NOT OK

Fault Code 343 active

Fault Code 343 inactive


Guided Step 2 – Check the power and ground connections.

Guided Step 2A – Check all engine and chassis power and ground connections.

Conditions

Turn keyswitch OFF.

Action

  • Corrosion
  • Loose connections.
OK NOT OK

Clean and tight. Measure within OEM specifications for voltage drop under electrical load

Repair damaged connections

 CAUTION 

To reduce the possibility of pin and harness damage, use the following test lead when taking a measurement:
Part Number 3822758 – male Deutsch/AMP/Metri-Pack test lead.

Guided Step 2B – Check all power and ground resistances.

Conditions

  • Turn keyswitch OFF.
  • Disconnect the actuator harness connector from the ECM.
  • Disconnect the unswitched battery 3-pin Weather-Pack connector.

Action

  • Measure the resistance from pin 22 of actuator harness connector to pin C of the battery connector.
  • Measure the resistance from pin 23 of actuator harness connector to pin C of the battery connector.
  • Measure the resistance from pin 20 of actuator harness connector to pin A of the battery connector.
  • Measure the resistance from pin 21 of actuator harness connector to pin A of the battery connector.
  • Measure the resistance from pin 9 of actuator harness connector to pin B of the battery connector.
  • Measure the resistance from pin 25 of actuator harness connector to pin B of the battery connector.
  • Measure the resistance from pin 27 of actuator harness connector to pin B of the battery connector.
OK NOT OK

Less than 10 ohms

Replace or replace the actuator harness.

Guided Step 2C – Check for good vehicle grounding.

Conditions

  • Turn keyswitch OFF.

Action

  • Check from negative (-) battery post to block ground
  • Check from block ground to negative (-) starter post ground
  • Check block to frame ground
  • Check block to cab ground.
OK NOT OK

Meets OEM specifications for voltage test under electrical load

Correct the vehicle grounds


Guided Step 3 – Check for moisture in the ECM connectors.

Guided Step 3A – Check for moisture in the ECM connectors.

Conditions

  • Turn keyswitch OFF.
  • Disconnect the engine harness connectors from the ECM.
OK NOT OK

All connectors dry

Dry the connectors

  • Dry the connector by using electrical contact cleaner, Part Number 3824510.
  • Replace the connector seal. Refer to Procedure 019-203.


Guided Step 4 – Check the engine position sensor.

 CAUTION 

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

Guided Step 4A – Check the engine position sensor for damage.

Conditions

  • Turn keyswitch OFF.
  • Disconnect the sensor harness from the engine position sensor.
  • Disconnect the sensor harness connector from ECM.
OK NOT OK

No damage

Replace the engine position sensor. Refer to Procedure 019-038.

 CAUTION 

To reduce the possibility of pin and harness damage, use the following test leads when taking a measurement:
Part Number 3822758 – male Deutsch/AMP/Metri-Pack test lead
Part Number 3823995 – female AMP/Metri-Pack test lead.

 CAUTION 

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

Guided Step 4B – Check the engine position sensor polarity.

Conditions

  • Turn keyswitch OFF.
  • Disconnect the sensor harness from the engine position sensor.
  • Disconnect the sensor harness connector from the ECM.

Action

  • Check for continuity between pin 11 of the sensor harness connector and pin A of the engine position sensor connector, harness side.
  • Check for continuity between pin 15 of the sensor harness connector and pin B of the engine position sensor connector, harness side.
  • Check for continuity between pin 1 of the sensor harness connector and pin C of the engine position sensor connector, harness side.
  • Check for continuity between pin 14 of the sensor harness connector and pin D of the engine position sensor connector, harness side.
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OK NOT OK

Less than 10 ohms

Correct the polarity by switching the necessary wires.

Guided Step 4C – Check alternator.

Conditions

  • Remove alternator belt.
  • Connect engine harness to ECM.

Action

  • Start engine.
OK NOT OK

Fault Code 343 inactive, repair or replace alternator. See manufacturing specifications.

Note: A capacitor across the alternator output
(observe proper polarity of capacitor), can help alternator-induced voltage spikes. Refer to OEM manufacturer for electrical specifications.

Fault Code 343 active

Guided Step 4D – Check engine brake circuit.

Conditions

  • Disconnect engine brake connector from engine harness.
  • Turn keyswitch ON.

Action

  • Start engine.
OK NOT OK

Fault Code 343 goes inactive.

  • Replace engine brake harness. Refer to Procedure 019-043.
  • Replace engine brake solenoid. Refer to Procedure 020-001 in either the Troubleshooting and Repair Manual, M11 Series Engines (STC, CELECT™, CELECT™ Plus models), Bulletin 3666139, or Troubleshooting and Repair Manual, N14 Series Engines
    (STC, CELECT™, CELECT™ Plus models), Bulletin 3666142.

Fault Code 343 active

 CAUTION 

To reduce the possibility of pin and harness damage, use the following test lead when taking a measurement:
Part Number 3822758 – male Deutsch/AMP/Metri-Pack test lead.

Guided Step 4E – Check datalink wiring.

Conditions

  • Turn keyswitch OFF.
  • Disconnect sensor and OEM ECM connectors from ECM.

Action

  • Measure from pin 27 of OEM connector at the ECM to engine block ground.
  • Measure from pin 8 of OEM connector at the ECM to engine block ground.
  • Measure from pin 10 of sensor connector at the ECM to engine block ground.
  • Measure from pin 20 of sensor connector at the ECM to engine block ground.
OK NOT OK

Fault Code 343 inactive

Less than 100k ohms

  • Repair or replace datalink wiring. Refer to Procedure 019-165 or 019-166.

Guided Step 4F – Check OEM components for shorting to ground.

Conditions

  • Turn keyswitch OFF.

Action

  • Disable or unplug OEM components that intermittently short to ground, such as fan clutch relays, the keyswitch, engine speed sensors in the flywheel, tachographs, engine brakes, vehicle speed sensors, the starter, datalinks, or the alternator.
OK NOT OK

Fault Code 343 inactive

  • Repair or replace that OEM component. Refer to the OEM manual for procedures.

Fault Code 343 active

Guided Step 4G – Check injector circuits for short to ground.

Conditions

  • Turn keyswitch OFF.
  • Disconnect actuator harness connector at the ECM.

Action

OK NOT OK

Fault Code 343 inactive

  • Repair or replace injector component that failed.

Fault Code 343 active

Guided Step 4H – Check fuel shutoff solenoid for short to ground or open circuit.

Conditions

  • Turn keyswitch OFF.
  • Disconnect fuel shutoff solenoid wire from fuel shutoff valve.
  • Disconnect the actuator harness connector at the ECM.

Action

  • Measure the resistance from pin 16 of the actuator harness to the fuel shutoff valve wire at the fuel shutoff valve solenoid.
OK NOT OK

Fault Code 343 inactive

  • Replace fuel shutoff valve solenoid. Refer to Procedure 019-050.

Fault Code 343 active

Guided Step 4I – Check the fuel shutoff solenoid for an open circuit.

Conditions

  • Turn keyswitch OFF.
  • Disconnect the fuel shutoff solenoid wire from the fuel shutoff valve.
  • Disconnect the actuator harness connector from the ECM.

Action

  • Measure from pin 16 at the actuator harness connector to all other pins in the connector.
OK NOT OK

Fault Code 343 inactive

Fault Code 343 active


Guided Step 5 – Clear the fault codes.

 CAUTION 

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

Guided Step 5A – Disable the fault code.

Conditions

  • Connect all the components.

Action

  • Start the engine and let idle for one minute.
  • Verify Fault Code 343 is inactive.
OK NOT OK

Fault Code 343 inactive

Replace the ECM. Refer to Procedure 019-031. Return to the troubleshooting steps or contact your nearest Cummins Authorized Repair Location if all the steps have been completed and checked again.

Guided Step 5B – Clear the inactive fault codes.

Action

  • Erase the inactive fault codes using INSITE™ electronic service tool.
OK NOT OK

All fault codes cleared

Troubleshoot any remaining active fault codes.

Repair complete

Appropriate troubleshooting chart

Last Modified:  08-Sep-2004