Camshaft Position Sensor (Secondary) - Abnormal Frequency, Pulse Width, or Period
What does CAT-CID342-FMI8 mean?
The CAT-CID342-FMI8 (Caterpillar) diesel fault code means: Camshaft Position Sensor (Secondary) - Abnormal Frequency, Pulse Width, or Period. This is a serious severity code.
Common Symptoms
- Check Engine Light
- Frequency or pulse width out of range
- Speed, crank, or cam signals dropping out
Probable Causes (Ranked by Likelihood)
- Damaged tone ring or target wheel Likely
- Sensor air gap incorrect or debris on tip Likely
- Wiring shield damaged causing signal noise Possible
Step-by-Step Diagnostic Procedure
Verify air gap at the sensor tip per CAT service manual.
Inspect the tone or target wheel for damage, debris, or missing teeth.
Scope the signal during cranking and running for missing pulses or noise.
Replace sensor, clean target, or repair wiring as indicated.
Frequently Asked Questions
What does CAT code CID342-FMI8 mean?
CAT code CID342-FMI8 (Camshaft Position Sensor (Secondary) - Abnormal Frequency, Pulse Width, or Period) is a serious-severity fault on Caterpillar on-highway diesel engines. CID 342 is the Camshaft Position Sensor (Secondary), measuring secondary camshaft speed and timing signal. FMI 8 (Abnormal Frequency, Pulse Width, or Period) indicates the specific fault mode. Use CAT ET to confirm before replacing parts. Diagnose with CAT ET (Electronic Technician) software.
Can I drive my truck with CAT code CID342-FMI8?
Short distances may be acceptable, but running long with this fault risks progressive damage or forced derate. Address promptly.
How much does it cost to fix CAT CID342-FMI8?
Typical repair is $250-$1200. Sensor / wiring fixes fall at the low end; injector, HEUI pump, turbo, or aftertreatment work falls at the high end. CAT dealer labor often requires CAT ET for calibration and parameter programming.