U1004: On Hyundai hybrids, U1004 is a CAN communication code for the hybrid control network, typically stored with U0293 lost communication with the hybrid powertrain control module

Hyundai hybrid CAN communication fault

Severity: Inspect soon

Owners report limp mode, a hybrid system that stops charging, dashboard lights all coming on at highway speed and ABS CAN time-outs with this code, so propulsion and braking support can be affected.

It gets more serious if:

Stop: Stop if the car goes into limp mode, loses power, stalls or every dash light comes on while driving: pull over safely and arrange a tow.

Source: how we rate severity

U1004 in short

On Hyundai Sonata Hybrids, U1004 is a hybrid CAN communication code, usually stored with U0293 for lost contact with the hybrid powertrain control module. Owners report limp mode, stalls and lights coming on, often with P1326. It needs a prompt check by a Hyundai technician.

The hybrid system uses its own CAN network so the engine, hybrid control unit, battery and motor controllers can talk. U1004 is stored when that communication breaks. A technician forum summary for a 2012 Sonata Hybrid ties it to lost communication with the hybrid control unit, and owners list it next to U0293. This page speaks only for Hyundai.

Four owners of 2012-2018 Sonata Hybrids list U1004 with P1326, Hyundai's knock sensor and engine protection code, and report limp mode, a hybrid that would not charge, three stalls in under two weeks and every dash light coming on at highway speed. One also listed ABS and motor control CAN time-out codes.

The sources do not say which part failed, so a technician needs to test before parts are replaced.

Pick your make

U1004 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.

U1004 on Hyundai

Most likely causes

Cause 1: Lost communication with the hybrid control unit
Supported by vehicle data
Why it ranks here
The technician forum summary and two owners tie U1004 to lost communication with the hybrid control unit, stored with U0293.
What would change this
Rises when U0293 is stored too and hybrid warnings come on. Falls if the hybrid unit answers a scan normally.
Cause 2: Engine protection mode after a P1326 event
Possible — needs testing
Why it ranks here
Several owners read U1004 with P1326 and believe the communication codes are secondary to the engine protection mode, but none of them has a repair confirming it.
What would change this
Rises when P1326 or engine failure signs come first. Falls if P1326 is absent.
Cause 3: CAN time-outs to the ABS, steering or transmission controller
Possible — needs testing
Why it ranks here
Owners list CAN time-out codes for the ABS, transmission, electric power steering and hybrid control unit with U1004.
What would change this
Rises when several systems log time-outs together. Falls if only one does.

What to test first

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

Step 1: Read all modules and note whether U0293, P1326 or CAN time-out codes are stored with U1004, and whether the car has gone into limp mode.
Low riskTool: scan tool that reads all modules
- IfU0293 is stored with it
  It meansHybrid control communication is the likely story; have a Hyundai technician test it.
  Go to step 2
- IfP1326 is stored first
  It meansThe engine protection side needs checking too.
  Go to step 2
Step 2: Have a Hyundai technician test the hybrid control unit, its power and ground, the CAN wiring and the engine protection history.
Best left to a shop
Warning:Hybrid cars contain high-voltage parts; leave testing to a trained technician.
- IfHybrid control communication fails
  It meansRepair per the maker procedure.
  Points to: Lost communication with the hybrid control unit
- IfSeveral controllers time out together
  It meansLook for a shared power or CAN fault.
  Points to: CAN time-outs to the ABS, steering or transmission controller

Symptoms

Hybrid system warning light
Limp mode or loss of power Gets more serious: stop and have it checked.
Stall while driving Gets more serious: stop and have it checked.
Many dash lights at once Gets more serious: stop and have it checked.

How to fix

On your vehicle

Hyundai

2012–2018 · Sonata
Supported by vehicle data
Owners and a technician summary report U1004 with U0293 on Sonata Hybrids, with limp mode and stalls.

All Module network (CAN bus) communication codes

U1004 questions

Does U1004 mean the same on other makes?

Not necessarily. This page covers Hyundai hybrids only; we have not sourced meanings for other makes.

Sources and review

U1004 dtc (IATN technician network summary) — International Automotive Technicians Network
NHTSA complaint ODI 11462848: 2018 Hyundai Sonata Hybrid — NHTSA (owner complaint)
NHTSA complaint ODI 11769494: 2014 Hyundai Sonata Hybrid — NHTSA (owner complaint)
NHTSA complaint ODI 11716603: 2017 Hyundai Sonata — NHTSA (owner complaint)
NHTSA complaint ODI 11732884: 2012 Hyundai Sonata — NHTSA (owner complaint)

Last reviewed: October 16, 2026
Written by: Saurabh K.
Editorial review: Pending
Technician review: Technician review pending

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

Severity: Inspect soon

Pick your make

Most likely causes

Cause 1: Lost communication with the hybrid control unit

Cause 2: Engine protection mode after a P1326 event

Cause 3: CAN time-outs to the ABS, steering or transmission controller

What to test first

Step 1: Read all modules and note whether U0293, P1326 or CAN time-out codes are stored with U1004, and whether the car has gone into limp mode.

Step 2: Have a Hyundai technician test the hybrid control unit, its power and ground, the CAN wiring and the engine protection history.