U2603 On the Chevrolet Volt, U2603 is the first of a block of codes set when the Battery Energy Control Module loses communication with the battery interface modules

Volt BECM lost communication (U2603-U2606, U2617-U2624)

U2603 in short

On the Chevrolet Volt, U2603 means the Battery Energy Control Module lost contact with the battery interface modules. It usually appears with U2604-U2606 and P1E00 and points to a failed module. The car can lose drive power or refuse to start, so have a dealer inspect it soon; this is not a home repair.

The Volt has a computer that supervises the high-voltage battery, the Battery Energy Control Module. It talks to interface modules on the battery over the vehicle network. When those messages stop, it stores U2603, and it normally stores the neighbouring codes too.

Owners and dealers describe the same pattern: U2603 through U2606 and U2617 through U2624 plus P1E00, a Propulsion Power Is Reduced message, and sometimes a car that will not shift out of park or charge. In the complaints here the repair was a new Battery Energy Control Module.

This page speaks only for Chevrolet. Other makes may use U2603 differently, and we have not sourced them.

Pick your make

U2603 is a manufacturer-specific code: its meaning depends on who built the car.

Other makes: meaning not verified. Check with a scan tool that reads manufacturer definitions.

Most likely causes

  1. Internal failure of the Battery Energy Control Module

    Supported by vehicle data
    Why it ranks here
    Owners across 2016-2018 Volts report this code block with a BECM replacement, and one dealer diagnosed an internal short in the BECM that cut off communication with the battery modules.
    What would change this
    Rises if a dealer confirms the fault by circuit testing or the whole code block returns after clearing. Falls if a connector or power or ground problem is found.

  2. Power, ground or connector problem at the module

    Possible — needs testing
    Why it ranks here
    Network codes do not say which part failed, and AA1Car says further testing is needed before repairs. No Volt complaint here names a wiring cause for this code block, so it ranks below the module.
    What would change this
    Rises if the codes appeared after battery or underhood work, or a connector is damaged. Falls if the module tests bad on its own.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Read every stored code with a scan tool that can read hybrid modules, and note whether the block U2603-U2606 and U2617-U2624 is stored together with P1E00.

    Low riskTool: scan tool that reads hybrid modules

    • IfThe whole block of battery interface communication codes is stored, with P1E00

      It meansOwner and dealer reports tie this pattern to the Battery Energy Control Module itself.

      Go to step 2

    • IfOnly one or two of the codes are stored, or they came after 12-volt battery work

      It meansHave the dealer check power, ground and connectors to the module before condemning it.

      Points to: Power, ground or connector problem at the module

  2. Have a Chevrolet dealer confirm the fault with circuit testing and ask whether any warranty or special coverage applies to your VIN.

    Best left to a shop

    Warning:The traction battery and its control module are high voltage. Only a trained technician should test or open them.

Symptoms

  • Propulsion Power Is Reduced message or a sudden drop in drive power Gets more serious: stop and have it checked.
  • Check engine light with several U26xx codes stored
  • Car will not shift out of park, will not charge or will not start
  • Stall while driving Gets more serious: stop and have it checked.

Compare with: Check engine light with loss of power

How to fix

This is a safety-critical system, so we explain the code but don't give repair steps. Have it inspected by a qualified technician.

On your vehicle

Chevrolet

  • 2016–2018 · Volt

    Supported by vehicle data

    Owners of 2016-2018 Volts report U2603 through U2624 with P1E00 and a BECM replacement. Owner complaints cite a GM bulletin (18-NA-261) and a special coverage; neither document was read, so treat both as unverified.

  • U2624On the Chevrolet Volt, U2624 is part of the Battery Energy Control Module communication code block, stored with U2603-U2606 and P1E00

    Shares causes Supported by vehicle data

    U2624 is part of the same BECM code block and is usually stored with U2603 on the Volt.

All Module network (CAN bus) communication codes

U2603 questions

Is it safe to drive with U2603 on a Volt?

Owners report sudden reduced power and stalls in traffic, so treat it as inspect-soon and stop if power drops while driving. We have not verified how often each car fails.

Does GM cover the BECM?

Owners cite a GM special coverage (N232432680) extending BECM coverage on 2016-2018 Volts to 15 years/150,000 miles. We have not verified the terms; ask a Chevrolet dealer to check your VIN.

Sources and review

  1. NHTSA complaint ODI 11745949: 2017 Chevrolet Volt — NHTSA (owner complaint)
  2. NHTSA complaint ODI 11766936: 2018 Chevrolet Volt — NHTSA (owner complaint)
  3. NHTSA complaint ODI 11752752: 2018 Chevrolet Volt — NHTSA (owner complaint)
  4. NHTSA complaint ODI 11582758: 2016 Chevrolet Volt — NHTSA (owner complaint)
  5. NHTSA complaint ODI 11669821: 2017 Chevrolet Volt — NHTSA (owner complaint)
  6. CAN bus U-codes — AA1Car Auto Diagnosis
  7. NHTSA complaint ODI 11706596: 2017 Chevrolet Volt — NHTSA (owner complaint)
Last reviewed
Written by
Saurabh K.
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This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error

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