U3005 Moderate Generic / SAE

U3005: Retained Accessory Power

Network and Communication Control Module Power and Ignition Supply

What to do

The obvious symptom is the radio not staying on after you switch off, or not switching off when you open the door. The expensive symptom is a flat battery.

If the car has needed jump starting after standing for a few days, mention that first. This circuit is meant to release after a timeout — one that never releases keeps the whole car awake and drains the battery, and that is the version of this fault worth paying to fix.

Ask them to check the door switches. The timer decides when to shut off by watching for a door opening, so a door switch that reports the door permanently closed leaves the car waiting forever. That is a cheap part and a common cause.

A quick check you can do: at night, with the car locked and standing, look for any interior or boot light staying on. That is often the visible end of the same problem.

What this code means

A module is reporting a problem with retained accessory power.

This range is different from every other network family, and the difference decides how it should be diagnosed.

U01xx and U02xx say a module went silent. U04xx and U05xx say a module is talking nonsense about something it watches. This range says a module is reporting a problem with its own foundations — its supply, its earth, or the ignition state that tells it whether the car is even meant to be awake.

Which makes these codes upstream of almost everything else. A module with a marginal earth does not fail cleanly; it reports implausible values about every sensor it reads, sets codes in unrelated systems, and drops off the bus intermittently. A scan tool showing thirty codes across five systems very often has one of these underneath it.

So read this family first and fix it first. Clearing a page of downstream codes before the supply fault is repaired produces a page of downstream codes again by the end of the week.

And start with the battery, genuinely. Not as a formality — a twelve-volt battery weak enough to sag during cranking, or a terminal with corrosion under a clamp that looks tight, reproduces this entire family exactly. It is the cheapest thing to eliminate and by some distance the most common cause.

Retained accessory power is the feature that keeps the radio and windows working after you switch off, until a door is opened — and it is a timed function, which is what makes it fail interestingly.

The car must decide when to stop. It holds the accessory circuits alive, watches for a door to open, and otherwise times out. A fault here therefore has two shapes, and one costs money.

The harmless one is the feature simply not working — the radio dies the instant the ignition goes off.

The expensive one is power that is never released. A car that keeps its accessory circuits energised does not go to sleep, and a car that does not sleep flattens its battery over a few days of standing. If yours has needed a jump start after a weekend, this code is a strong candidate for why.

Door switches are the usual physical cause, because the timer's whole logic depends on knowing whether a door has opened. A switch reporting a door permanently shut leaves the car waiting for an event that never comes — which is why this code and a door switch code together are one fault, and the door switch is the one to fix.

Likely causes

Start here

Low system voltage · easy
Corroded earth connection · moderate
Blown fuse or failed supply · easy
Failed power or earth supply to the module · moderate
Corroded or loose connector · easy

Less common

Damaged wiring harness · moderate
Faulty body control module · specialist

Symptoms

Components involved

Information, not instruction

CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.

Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.

Community experience

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The car — make, model, year and engine. The same fault behaves differently on each.
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