Electronic Control System Signature, ISX and QSX15 Engines – FAULT CODE 121

Crankshaft Engine Position Sensor Circuit


Overview

CODE REASON EFFECT
Fault Code: 121
PID: P190
SPN: 190
FMI: 10/10
LAMP: Yellow
SRT: 

No engine speed signal detected from the crankshaft engine position sensor.

Hard starting, low power, rough idle, or possible white smoke.

Crankshaft Engine Position Sensor Circuit
SMALL | MEDIUM | LARGE

Circuit Description

The crankshaft engine position sensor provides engine speed and position information to the electronic control module (ECM). The sensor
must be powered up by (+) 5-VDC to operate. The sensor generates the signal by sensing the movement of target teeth machined into a tone wheel that is mounted to the crankshaft.

Component Location

The crankshaft engine position sensor is located on the side of the front cover on the intake side of the engine.
Refer to Procedure 100-002 (Engine Diagrams in Section E for component location.

Shop Talk

Possible causes of this fault code include a damaged crankshaft engine position sensor, an open or a short circuit, or power supply voltage failure.

Refer to Troubleshooting Fault Code t05-121.

Last Modified:  26-Oct-2010