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Overview
Circuit Description
The engine position sensor monitors the engine position and the engine speed and passes this information to the fuel control module through the engine harness. The fuel control module processes the engine speed and sends the engine speed to the electronic control module (ECM).
Component Location
The engine position sensor is located above the accessory drive in the rear face of the gear housing on the fuel system side of the engine.
FAULT CODE 121
Engine Speed/Position Sensor Circuit
CODE REASON EFFECT
Fault Code: 121 PID: P190 SPN: 190 FMI: 10/10 LAMP: Amber SRT:
Engine Speed/Position Sensor Circuit - lost one of two signals from the magnetic pickup sensor.
None on performance.
Engine Speed/Position Sensor Circuit
Shop Talk
If the fault occurs only at a certain engine temperature, check the engine position sensor circuit while the engine is at that particular temperature.
Check the camshaft end play to make sure the camshaft gear is not moving too far away from the end of the engine position sensor.
Check for moisture in the sensor harness connector at the fuel control module.
Possible causes for this fault include a damaged engine position sensor, a short circuit to ground, or an open circuit.
Cautions and Warnings
Troubleshooting Steps
CAUTION
To avoid damaging a new ECM, all other active fault codes must be investigated prior to replacing the ECM.
CAUTION
To avoid 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 3823996 - female Weather-Pack test lead.
CAUTION
To avoid pin and harness damage, use the following test lead when taking a measurement:
Part Number 3823996 - female Weather-Pack test lead.
CAUTION
To avoid pin and harness damage, use the following test lead when taking a measurement:
Part Number 3822758 - male Deutsch/AMP/Metri-Pack test lead.
STEPS SPECIFICATIONS
Guided Step 1 - Check the engine position sensor
Guided Step 1A - Inspect the engine position sensor and the engine harness connectors.
STEP 1. Check the engine position sensor STEP 1A. Inspect the engine
position sensor and engine harness connectors
Dirty or damaged pins?
STEP 1B. Check for a short circuit to ground
More than 100k ohms?
STEP 1C. Inspect the engine position sensor
Damaged engine position sensor?
STEP 1D. Check the resistance of the engine position sensor
1000 to 2000 ohms?
STEP 1E. Check for a short circuit between the coils
More than 100k ohms?
STEP 2. Check the sensor harness and the fuel control module connector pins STEP 2A. Inspect the sensor
harness and the fuel control module connector pins
Dirty or damaged pins?
STEP 2B. Check for a short circuit to ground
More than 100k ohms?
STEP 2C. Check for a short circuit from pin to pin
More than 100k ohms?
STEP 2D. Check for an open circuit 1000 to 2000 ohms?
STEP 3. Clear the fault codes
STEP 3A. Disable the fault code Fault Code 121 inactive?
STEP 3B. Clear the inactive fault codes
All fault codes cleared?
Conditions
Guided Step 1B - Check for a short circuit to ground.
Turn keyswitch OFF.
Disconnect the engine harness from the engine position sensor.
Action
Inspect the engine position sensor and the engine harness connector pins for the following:
Corroded pins
Bent or broken pins
Pushed back or expanded pins
Moisture in or on the connector
Missing or damaged connector seals
Dirt or debris in or on the connector pins.
For general inspection techniques, refer to Component Connector and Pin Inspection, Procedure 019-361.
Dirty or damaged pins? Dirty or damaged pins?
YES NO
Repair the damaged pins.
Repair or replace the engine harness or sensor, whichever has the damaged pins.
Flush the dirt, debris, or moisture from the connector pins using electrical contact cleaner, Part Number 3824510.
Install the appropriate connector seal if it is damaged or missing.
Repair or replace the engine harness.
Refer to Procedure 019-043.
Replace the engine position sensor.
Refer to Procedure 019-038.
No Repair
Go to 3A Go to 1B
CAUTION
Guided Step 1C - Inspect the engine position sensor.
To avoid pin and harness damage, use the following test lead when taking a measurement:
Part Number 3823996 - female Weather-Pack test lead.
Conditions
Turn keyswitch OFF.
Disconnect the sensor harness from the engine position sensor.
Action
Check for a short circuit to ground.
Measure the resistance from the engine position sensor number 1 SIGNAL (+) pin of the sensor connector to engine block ground.
Measure the resistance from the engine position sensor number 1 SIGNAL (-) pin of the sensor connector to engine block ground.
Refer to the wiring diagram for connector pin identification.
For general resistance measurement techniques, refer to the Resistance Measurements Using a Multimeter and Wiring Diagram, Procedure 019-360.
More than 100k ohms? More than 100k ohms?
YES NO
No Repair
Replace the engine position sensor.
Refer to Procedure 019-038.
Go to 1C Go to 3A
Conditions
Turn keyswitch OFF.
Disconnect the sensor harness from
Guided Step 1D - Check the resistance of the engine position sensor.
the engine position sensor.
Action
Inspect the engine position sensor and the connector pins for the following:
Corroded pins
Bent or broken pins
Pushed back or expanded pins
Moisture in or on the connector
Missing or damaged connector seals
Dirt or debris in or on the connector pins.
For general inspection techniques, refer to Component Connector and Pin Inspection, Procedure 019-361.
Dirty or damaged pins? Dirty or damaged pins?
YES NO
Repair the damaged pins.
Repair or replace the engine harness or sensor, whichever has the damaged pins.
Flush the dirt, debris, or moisture from the connector pins using electrical contact cleaner, Part Number 3824510.
Install the appropriate connector seal if it is damaged or missing.
Replace the engine harness. Refer to Procedure 019-043.
Replace the engine position sensor.
Refer to Procedure 019-038.
No Repair
Go to 3A Go to 1D
CAUTION
To avoid pin and harness damage, use the following test lead when taking a measurement:
Part Number 3823996 - female Weather-Pack test lead.
Guided Step 1E - Check for a short circuit between the coils.
Conditions
Turn keyswitch OFF.
Disconnect the sensor harness from the engine position sensor.
Action
Check the resistance of the engine position sensor.
Measure the resistance from the engine position sensor number 1 SIGNAL (+) pin to the engine position sensor number 1 SIGNAL (-) pin of the engine position sensor.
Measure the resistance from the engine position sensor number 2 SIGNAL (-) pin to the engine position sensor number 2 SIGNAL (+) pin of the engine position sensor.
Refer to the wiring diagram for connector pin identification.
For general resistance measurement techniques, refer to the Resistance Measurements Using a Multimeter and Wiring Diagram, Procedure 019-360.
1000 to 2000 ohms? 1000 to 2000 ohms?
YES NO
No Repair
Replace the engine position sensor.
Refer to Procedure 019-038.
Go to 1E Go to 3A
CAUTION
To avoid pin and harness damage, use the following test lead when taking a measurement:
Guided Step 2 - Check the sensor harness
Guided Step 2A - Inspect the sensor harness and the fuel control module connector pins.
Part Number 3823996 - female Weather-Pack test lead.
Conditions
Turn keyswitch OFF.
Disconnect the engine harness from the engine position sensor.
Action
Check for a short circuit between the coils.
Measure the resistance from the engine position sensor number 1 SIGNAL (+) pin to the engine position sensor number 1 SIGNAL (-) pin of the engine position sensor.
Refer to the wiring diagram for connector pin identification.
For general resistance measurement techniques, refer to the Resistance Measurements Using a Multimeter and Wiring Diagram, Procedure 019-360.
More than 100k ohms? More than 100k ohms?
YES NO
No Repair
Replace the engine position sensor.
Refer to Procedure 019-038.
Go to 2A Go to 3A
CAUTION
To avoid damaging a new ECM, all other active fault codes must be investigated prior to replacing the ECM.
Conditions
Turn keyswitch OFF.
Disconnect the sensor harness
connector from the fuel control module.
Action
Inspect the sensor harness and the fuel control module connector pins for the following:
Corroded pins
Bent or broken pins
Pushed back or expanded pins
Moisture in or on the connector
Missing or damaged connector seals
Dirt or debris in or on the connector pins.
For general inspection techniques, refer to Component Connector and Pin Inspection, Procedure 019-361.
Dirty or damaged pins? Dirty or damaged pins?
YES NO
Repair the damaged pins
Repair or replace the engine harness or fuel control module, whichever has the damaged pins.
Flush the dirt, debris, or moisture from the connector pins using electrical contact cleaner, Part Number 3824510.
Install the appropriate connector seal if it is damaged or missing.
Replace the engine harness. Refer to Procedure 019-043.
Replace the fuel control module. Call for authorization.
No Repair
Go to 3A Go to 2B
Guided Step 2B - Check for a short circuit to ground.
CAUTION
To avoid pin and harness damage, use the following test lead when taking a measurement:
Part Number 3822758 - male Deutsch/AMP/Metri-Pack test lead.
Conditions
Turn keyswitch OFF.
Disconnect the sensor harness connector from the fuel control module.
Disconnect the sensor harness from the engine position sensor.
Action
Check for a short circuit to ground.
Measure the
resistance from the engine position sensor number 1 SIGNAL (+) pin of the sensor harness connector to engine block ground.
Measure the resistance from engine position sensor number 2 SIGNAL (+) pin of the sensor harness connector to engine block ground.
Refer to the wiring
diagram or circuit diagram for connector pin
SMALL | MEDIUM | LARGE
Guided Step 2C - Check for a short circuit from pin to pin.
identification.
For general resistance measurement techniques, refer to the Resistance Measurements Using a Multimeter and Wiring Diagram, Procedure 019- 360.
More than 100k ohms? More than 100k ohms?
YES NO
No Repair
Repair or replace the engine harness.
Refer to Procedure 019-043.
Go to 2C Go to 3A
CAUTION
To avoid pin and harness damage, use the following test lead when taking a measurement:
Part Number 3822758 - male Deutsch/AMP/Metri-Pack test lead.
Conditions
Turn keyswitch OFF.
Disconnect the sensor harness connector from the fuel control module.
Disconnect the sensor harness from the engine position sensor.
Action
Check for a short circuit from pin to pin.
SMALL | MEDIUM | LARGE
Measure the resistance from engine position sensor number 1 SIGNAL (+) pin of the sensor harness connector to all other pins in the connector.
Measure the resistance from engine position sensor number 1 SIGNAL (-) pin of the sensor harness connector to all other pins in the connector.
Measure the resistance from engine position sensor number 2 SIGNAL (-) pin of the sensor harness connector to all other pins in the connector.
Measure the resistance from engine position sensor number 2 SIGNAL (+) pin of the sensor harness connector to all other pins in the connector.
Refer to the wiring
diagram or circuit diagram for connector pin
identification.
For general resistance measurement techniques, refer to the Resistance Measurements Using a Multimeter and Wiring Diagram, Procedure 019- 360.
Guided Step 2D - Check for an open circuit.
More than 100k ohms?
YES NO
No Repair
Repair or replace the engine harness.
Replace the engine harness. Refer to Procedure 019-043.
Go to 2D Go to 3A
CAUTION
To avoid pin and harness damage, use the following test lead when taking a measurement:
Part Number 3822758 - male Deutsch/AMP/Metri-Pack test lead.
Conditions
Turn keyswitch OFF.
Disconnect the sensor harness
connector from the fuel control module.
Connect the sensor harness to the engine position sensor.
Action
Check for an open circuit.
Measure the resistance from engine position sensor number 2 SIGNAL (-) pin to engine position sensor number 2 SIGNAL (+) pin of the sensor harness connector.
Measure the resistance from engine position sensor number 1 SIGNAL (+) pin to engine position sensor number 1 SIGNAL (-) pin of the sensor harness connector.
Refer to the wiring diagram or circuit diagram for connector pin identification.
For general resistance measurement techniques, refer to the Resistance
Guided Step 3 - Clear the fault codes
Guided Step 3A - Disable the fault code.
Guided Step 3B - Clear the inactive fault codes.
Measurements Using a Multimeter and Wiring Diagram, Procedure 019-360.
1000 to 2000 ohms? 1000 to 2000 ohms?
YES NO
No Repair
Repair or replace the engine harness.
Replace the engine harness. Refer to Procedure 019-043.
Go to 3A Go to 3A
Conditions
Connect all components.
Turn keyswitch ON.
Action
Disable the fault code.
Start the engine and let it idle for 1 minute.
Use INSITE™ electronic service tool to verify Fault Code 121 is inactive.
Fault Code 121 inactive? Fault Code 121 inactive?
YES NO
No Repair
Return to the troubleshooting steps or contact your local Cummins Authorized Repair
Location if all the steps have been completed and checked again.
Go to 3B Go to 1A
Last Modified: 07-Feb-2005
Copyright © 2000-2009 Cummins Inc. All rights reserved.
Conditions
Connect all components.
Turn keyswitch ON.
Action
Clear the inactive fault codes.
Use INSITE™ electronic service tool to erase the inactive fault codes.
All fault codes cleared? All fault codes cleared?
YES NO
No Repair Troubleshoot any remaining active fault
codes.
Repair complete Appropriate troubleshooting charts
