CKP Sensor Signal Erratic (Nissan)
What does P1668 mean?
The P1668 code means the vehicle's onboard diagnostic system has detected: CKP Sensor Signal Erratic (Nissan). This is a critical severity code.
Common Symptoms
- Engine no start or intermittent no start
- Engine stalling while driving
- Severe misfires
- Check Engine Light flashing
- Tachometer erratic or dropping to zero
Probable Causes (Ranked by Likelihood)
- Faulty crankshaft position sensor Very High
- Damaged or missing teeth on crank reluctor wheel High
- Sensor air gap too large due to wear Moderate
- Wiring harness damage near exhaust or accessories Moderate
Step-by-Step Diagnostic Procedure
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Attempt to start the engine and check for RPM signal on the scan tool. No RPM reading confirms CKP failure.
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Inspect the CKP sensor for physical damage, oil contamination, or metallic debris on the magnetic tip.
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Measure CKP sensor resistance (check Nissan specs, typically 400-600 ohms for magnetic type).
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View CKP waveform on oscilloscope during cranking; look for uniform signal amplitude and missing tooth pattern.
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Inspect the crankshaft reluctor ring through the sensor mounting hole for damaged or missing teeth.
Frequently Asked Questions
Why will my Nissan not start with P1668?
The crankshaft position sensor provides the primary timing reference for fuel injection and ignition. Without a reliable signal, the ECU cannot fire the spark plugs or injectors.
Can heat cause CKP sensor failure?
Yes. CKP sensors are mounted near the engine block and are exposed to extreme heat. Thermal stress can cause intermittent failures that worsen when hot.
Is the CKP sensor hard to replace?
On most Nissan models it is accessible from underneath the vehicle near the transmission bellhousing. Replacement typically takes 30-60 minutes.