2008 Cummins Inc., Box 3005, Columbus, IN 47202-3005 U.S.A. Printed from QuickServe Online.All Rights Reserved. Last Modified: 02-Mar-2011

File: 79-fc121 Page 1 of 2Fault Code 121

Engine Position Sensor Circuit (EPS)CODES REASON EFFECT

Fault Code: 121PID(P), SID(S): 190SPN: 190FMI: 10Lamp: YellowSRT: 00-081

No engine speed signal detectedat one pair of pins, either pins 1and 15 or pins 11 and 14 of sensorharness.

None on performance.

Engine Position Sensor Circuit (EPS)

Circuit Description:The engine position circuit monitors the engine position and the engine speed and passes this information to the electroniccontrol module (ECM) through the sensor harness.

Component Location:M11 - The engine position circuit is located above the accessory drive.N14 - The engine position circuit is located at the back side of the gear housing flange on the cylinder block, just abovethe lubrication pump.

Shop Talk:If the fault occurs only at a certain engine temperature, check the engine position circuit while the engine is at thatparticular temperature.Check the camshaft end play to make sure the camshaft gear is not moving too far away from the end of the engineposition circuit.Check for moisture in the sensor harness connector at the ECM.If the engine runs rough, check that the engine position circuit is wired with proper polarity. Correct ECM to engine positioncircuit pin-to-pin wiring must be observed.

Refer to Troubleshooting Fault Code t05-121

2008 Cummins Inc., Box 3005, Columbus, IN 47202-3005 U.S.A. Printed from QuickServe Online.All Rights Reserved. Last Modified: 02-Mar-2011

File: 79-fc121 Page 2 of 2