Fault Processing Computer (FPC) Chip
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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
![]() ![]() To reduce the possibility of pin and harness damage, use the following test leads when taking a measurement: |
![]() ![]() To reduce the possibility of damaging a new ECM, all other active fault codes must be investigated prior to replacing the ECM. |
![]() ![]() To reduce the possibility of pin and harness damage, use the following test lead when taking a measurement: |
Troubleshooting Steps
STEPS | SPECIFICATIONS | |
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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. | |
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ConditionsTurn keyswitch ON. Action
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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. | |
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ConditionsTurn keyswitch OFF. Action
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OK | NOT OK |
Clean and tight. Measure within OEM specifications for voltage drop under electrical load |
Repair damaged connections |
![]() ![]() To reduce the possibility of pin and harness damage, use the following test lead when taking a measurement: |
Guided Step 2B – Check all power and ground resistances. | |
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Conditions
Action
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OK | NOT OK |
Less than 10 ohms |
Replace or replace the actuator harness. |
Guided Step 2C – Check for good vehicle grounding. | |
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Conditions
Action
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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. | |
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Conditions
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OK | NOT OK |
All connectors dry |
Dry the connectors
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Guided Step 4 – Check the engine position sensor.
![]() ![]() 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. | |
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Conditions
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|
OK | NOT OK |
No damage |
Replace the engine position sensor. Refer to Procedure 019-038. |
![]() ![]() To reduce the possibility of pin and harness damage, use the following test leads when taking a measurement: |
![]() ![]() 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. | ||
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Conditions
Action
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OK | NOT OK | |
Less than 10 ohms |
Correct the polarity by switching the necessary wires. |
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Guided Step 4C – Check alternator. | |
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Conditions
Action
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OK | NOT OK |
Fault Code 343 inactive, repair or replace alternator. See manufacturing specifications. Note: A capacitor across the alternator output |
Fault Code 343 active |
Guided Step 4D – Check engine brake circuit. | |
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Conditions
Action
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OK | NOT OK |
Fault Code 343 goes inactive.
|
Fault Code 343 active |
![]() ![]() To reduce the possibility of pin and harness damage, use the following test lead when taking a measurement: |
Guided Step 4E – Check datalink wiring. | |
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Conditions
Action
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OK | NOT OK |
Fault Code 343 inactive |
Less than 100k ohms |
Guided Step 4F – Check OEM components for shorting to ground. | |
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Conditions
Action
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OK | NOT OK |
Fault Code 343 inactive
|
Fault Code 343 active |
Guided Step 4G – Check injector circuits for short to ground. | |
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Conditions
Action
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OK | NOT OK |
Fault Code 343 inactive
|
Fault Code 343 active |
Guided Step 4H – Check fuel shutoff solenoid for short to ground or open circuit. | |
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Conditions
Action
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OK | NOT OK |
Fault Code 343 inactive
|
Fault Code 343 active |
Guided Step 4I – Check the fuel shutoff solenoid for an open circuit. | |
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Conditions
Action
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|
OK | NOT OK |
Fault Code 343 inactive |
Fault Code 343 active |
Guided Step 5 – Clear the fault codes.
![]() ![]() 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. | |
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Conditions
Action
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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. | |
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Action
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OK | NOT OK |
All fault codes cleared |
Troubleshoot any remaining active fault codes. |
Repair complete
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Appropriate troubleshooting chart
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