P0645 on Honda
A/C Clutch Relay Control Circuit
P0645 on Honda vehicles indicates a/c clutch relay control circuit. Au7o has documented this code across 2 Honda models — most commonly on Accord, Pilot. A general fault in the A/C compressor clutch relay control circuit driven by the control module. The commanded relay state does not match the measured circuit condition. Typical repair costs on Honda range from $250 to $900, depending on the specific model and root cause.
Common Causes of P0645
- •Faulty A/C clutch relay
- •Open or short in the relay control circuit
- •Corroded/damaged connectors
- •Blown fuse
- •Internal PCM driver fault
P0645 on Honda by Model
Honda Accord(1 issue)
- A/C Compressor Clutch Will Not Engage (Coil Failure / Excess Air Gap)2008-2012
8th generation Accords (especially V6) commonly lose A/C because the compressor clutch fails to engage. The magnetic clutch coil opens (loses continuity) or the clutch air gap widens with wear, so the clutch plate no longer pulls in when the A/C is requested - the compressor pulley spins but the compressor never turns. A failed high/low pressure switch or the 7.5A MG-clutch fuse can produce the same no-engage symptom. The result is warm air from the vents even with a full refrigerant charge. This is the compressor-clutch engagement failure, distinct from the refrigerant-loss condenser-leak issue.
Honda Pilot(1 issue)
- AC Clutch Relay Failure Causing No Cold Air or Battery Drain2016-2022
The Omron A/C clutch relay (Honda part 39794-SDA-A03) is defective and gets hot, causing failure. Honda-specific part with reduced coil current known to be problematic. When relay fails, either battery dies overnight (relay stuck closed) or AC stops working (relay stuck open). Low refrigerant from pressure relief valve venting can lead to failed AC compressor.
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View P0645 across all makes →Frequently Asked Questions
What does P0645 mean on Honda?▼
P0645 stands for "A/C Clutch Relay Control Circuit." A general fault in the A/C compressor clutch relay control circuit driven by the control module. The commanded relay state does not match the measured circuit condition. On Honda specifically, this code is documented across 2 models.
What causes P0645 on Honda vehicles?▼
Common causes on Honda: Faulty A/C clutch relay, Open or short in the relay control circuit, Corroded/damaged connectors, Blown fuse, Internal PCM driver fault. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0645 on a Honda?▼
Repair costs on Honda range from $250 to $900, depending on the specific model and root cause.
Which Honda models have P0645 documented?▼
Au7o has documented P0645 on 2 Honda models: Accord, Pilot.