P2C21: Engine Oil Temperature Sensor A/B Correlation

What it means

The signals of engine oil temperature sensors A and B do not correlate within the calibrated tolerance. One sensor drifts or installation offset between the two channels.

At a glance

• Usually lights the check-engine light

How it works

Engine oil temperature sensors A and B provide separate temperature readings that the control module compares for plausibility. This code sets when their readings differ beyond the allowed correlation range, which can happen if one sensor has drifted or the channels are connected to the wrong sensors.

Common causes

Most likely first.

1. One sensor characteristic drifted
2. Harness incorrectly swapped between channels

Symptoms

• Check-engine light
• Engine temperature reading may be inaccurate

How to diagnose it

1. Save freeze-frame data and compare the A and B oil temperature readings, noting whether the engine was cold or warm when the mismatch occurred.
2. After the vehicle has sat long enough to cool, compare both readings with ambient temperature and with each other for an implausible offset.
3. Inspect both oil temperature sensor connectors and harness branches for corrosion, damage, or signs that the A and B connections were swapped.
4. Check each sensor's live reading as the engine warms to see whether one channel drifts or responds differently from the other.
5. Test both sensor circuits and sensor outputs using the manufacturer's procedure to identify a wiring fault, swapped harness, or drifting sensor.

Common fixes

• Reconnect the A and B harness branches to their correct sensors if they were swapped.
• Repair a damaged or corroded sensor connector or wiring branch.
• Replace the sensor that fails the manufacturer's temperature-response test.

Can I keep driving?

If the engine otherwise runs normally, short trips may be possible, but monitor for oil temperature warnings and avoid sustained heavy loads. An inaccurate reading can prevent reliable temperature monitoring.