CM850 Electronic Control System – FAULT CODE 2321

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Overview

Engine Speed/Position Sensor Number 1 Circuit SMALL | MEDIUM | LARGE

Circuit Description

The crankshaft engine speed sensor provides engine speed information to the electronic control module (ECM). The sensor is powered by +5 VDC. 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 engine speed sensor is located on the intake side of the engine between number 5 and number 6 cylinders at the crankshaft level. For ISB and QSB5.9 the crankshaft engine speed sensor is located on the intake side of the engine behind the vibration damper near the tone wheel. Refer to Procedure 100-002 for a detailed component location view.

Shop Talk

During engine operation, the electronic control module (ECM) monitors the primary speed sensor (crankshaft speed sensor) signal. Fault Code 689 will become active and light the yellow lamp (marine does not
use lamps) if the signal from the primary speed sensor is not
present or degraded for more than three continuous seconds. Meanwhile, if the primary engine speed sensor signal is not present or is degraded for a moment (less than three seconds), the ECM will interrupt injection events based on the primary engine speed sensor and resume injection events using the backup engine speed sensor. Engine power will be reduced while the injection events are based on the backup speed sensor. If the primary speed sensor signal returns, the ECM will automatically interrupt injection events based on the backup speed sensor and resume injection events based on the primary speed sensor. If over a period of time, the ECM detects several incidents of a loss of the primary speed sensor signal, this fault code will become active.

A vehicle operator can notice an intermittent “misfire”
if the injection events are interrupted while the ECM switches from control based on the primary and secondary speed sensors. Also, a vehicle operator can notice intermittent “low power” if a “glitch”
in the primary speed sensor signal causes the engine to intermittently use the backup speed sensor for injection control.

This fault code becomes active whenever the ECM detects a persistent loss of the primary engine speed sensor signal over a short period of time.

This fault becomes inactive at each key-on or if the ECM does not detect a loss of the primary engine speed sensor signal for at least 20 minutes.

Failures that can cause this fault:

• Intermittent loss of primary speed sensor signal, the most likely cause is an intermittent open or short circuit can be experienced with speed sensor connector problems
• Sensor air gap that is marginally too small or too large.

Actions to take if this fault is intermittent:

• Look for intermittent engine harness connections in the primary engine speed sensor circuit
• Look for loose connections at the ECM connector where the pins can not be locked into the socket
• Look for places where the engine harness has worn into a nearby component causing an intermittent short circuit
• Look for pin wear at the speed sensor
• Inspect the target wheel for damage.

Refer to Troubleshooting Fault Code t05-2321