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P0645 Generic (SAE) Basic entry

A/C Clutch Relay Control Circuit

Updated 2026-10-02 · Computer & output circuits

Severity
Medium
Typical repair cost
60 – 500 EUR
System
Powertrain

What it means

P0645 is defined as "A/C Clutch Relay Control Circuit". the engine control module stores it when the monitored condition for this component or system is outside the limits programmed by the manufacturer.

This entry is compiled automatically from the standard definition and typical diagnostic practice for this type of fault. A detailed, reviewed article is in preparation.

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Symptoms

  • Check engine light on
  • Engine may not start or runs in limp mode
  • Several unrelated codes stored at once
  • Erratic gauge or warning light behaviour

Common causes

  1. A/C Clutch Relay Control Circuit worn, contaminated or out of calibration
  2. Mechanical problem in the system the sensor measures
  3. Air, vacuum or exhaust leak influencing the reading
  4. Wrong or low-quality replacement part
  5. Wiring resistance causing a small voltage offset

How to diagnose

  1. Compare the live A/C Clutch Relay Control Circuit reading with a known-good value or a second sensor at idle and at 2500 rpm
  2. Check for air, vacuum or exhaust leaks that could skew the reading
  3. Inspect the component for contamination and clean it if the design allows
  4. Verify the part number is correct for the engine
  5. Replace the A/C Clutch Relay Control Circuit if the reading remains out of specification

Frequently asked questions

Can I keep driving with P0645?

Usually yes for a short time, but expect reduced performance or higher fuel use. Have it diagnosed within a few days.

Will clearing P0645 fix it?

No. Clearing only erases the stored code; it returns as soon as the monitor runs again unless the cause is repaired.

Symptoms linked to this code

Terms to know

A/C compressorA/C pressure sensor / switch

Related codes

P0643P0644P0646P0647

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