Cause
Faulty module power relay
The relay that feeds a control module and the actuators hanging off it — often called the main or powertrain relay. Its failures are disproportionately confusing because one relay serves many circuits, so when it degrades, a group of entirely unrelated components all report faults at once and none of them is broken.
The characteristic failure is not a clean break but contact erosion. Every switching cycle draws a small arc, which pits and oxidises the contact faces; over years the resistance across them climbs. A relay in that state works perfectly at low load and collapses under high load, which is why the faults appear under acceleration, with the air conditioning on, or on a hot day — and vanish before the vehicle reaches a workshop.
That is also why it is missed: swapping in a known-good relay and finding the fault gone proves nothing if the fault was intermittent anyway, and a resistance check across the contacts reads fine because a multimeter passes a milliamp where the circuit passes amps. The test that finds it is voltage drop across the relay while the circuit is loaded.
The opposite failure is contacts welding closed, leaving the circuit permanently live — which shows up as unexplained battery drain and, on heater circuits, as components powered when nothing intends them to be.
When several unrelated codes appear together, look at what they share electrically rather than mechanically. This relay is very often the answer, and it is among the cheapest parts on the vehicle.
Typically specialist work. Needs equipment or training most home workshops do not have.
Codes this can cause (21)
Codes where this is a likely explanation first, rather than merely a possible one.
- P0EC6 Air Conditioning Power Supply Relay Control Circuit/Open Likely for this code Moderate
- P0EC7 Air Conditioning Power Supply Relay Control Circuit Low Likely for this code Moderate
- P0EC8 Air Conditioning Power Supply Relay Control Circuit High Likely for this code Moderate
- P2669 Actuator Supply Voltage B Circuit/Open Likely for this code High
- P2670 Actuator Supply Voltage B Circuit Low Likely for this code High
- P2671 Actuator Supply Voltage B Circuit High Likely for this code High
- P2684 Actuator Supply Voltage C Circuit/Open Likely for this code High
- P2685 Actuator Supply Voltage C Circuit Low Likely for this code High
- P2A32 AFCM Power Relay Control Circuit/Open Likely for this code High
- P2A33 AFCM Power Relay Control Circuit Low Likely for this code High
- P2A34 AFCM Power Relay Control Circuit High Likely for this code High
- P2A35 AFCM Power Relay Sense Circuit Likely for this code High
- P2A36 AFCM Power Relay Sense Circuit Low Likely for this code High
- P2A37 AFCM Power Relay Sense Circuit High Likely for this code High
- U3004 Accessory Power Relay Likely for this code Moderate
- P0D33 DC/DC Converter Current High High
- P0E0F Generator Inverter Power Supply A Circuit/Open High
- P0E10 Generator Inverter Power Supply A Circuit Low High
- P0E11 Generator Inverter Power Supply A Circuit High High
- P2610 Engine Control Module Internal Engine Off Timer Performance Moderate
- P2686 Actuator Supply Voltage C Circuit High High
Information, not instruction
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