U0071 — Vehicle Area Network (VAN) Data Bus E (-) – Voltage High #

Note: The wording of code U0071 may differ depending on the vehicle manufacturer (OEM). Always refer to your vehicle’s service manual for the most accurate description.

• U0071: Communication Bus E Off (Honda)
• U0071: Control Module Communication Bus “A” Off (GM, Ford)
• U0071: CAN Communication Line Error (Toyota)
• U0071: VAN Data Bus High (Renault, PSA)

Code Summary for U0071 #

U0071 is a generic OBD-II code that indicates a high voltage condition on the Vehicle Area Network (VAN) Data Bus E (-). The VAN is a communication pathway that allows various modules—like the Engine Control Module (ECM), Transmission Control Module (TCM), and Body Control Module (BCM)—to share data and commands. When the voltage on this communication line is abnormally high, it means modules may struggle to send or receive information correctly. This can lead to a range of electrical and drivability issues, depending on which systems rely on the affected data network. Prompt diagnosis and repair are essential to prevent further complications.

Common Symptoms for U0071 #

When U0071 is stored in your vehicle’s memory, you may notice symptoms that vary from subtle electrical irregularities to major functional problems. The extent of the symptoms often depends on which modules communicate over the affected network and how critical their functions are to the vehicle’s operation.

• Warning lights (Check Engine, ABS, traction control, etc.) appear on the dashboard
• Loss of communication with one or more modules during diagnostics
• Intermittent or complete failure of systems like ABS, ESP, or power steering
• Unresponsive or erratic electronic functions (windows, locks, HVAC)
• Vehicle may enter “limp” or “safe” mode
• Occasional no-start conditions

Most Likely Causes for U0071 #

The U0071 code generally points to a problem with the communication wiring or a module on the VAN network. High voltage on the negative line suggests either a wiring fault or a module that’s malfunctioning and sending unintended voltage into the network. Below is a ranked list of probable causes, from most to least common:

1. Short to power in the VAN Data Bus E (-) wiring harness
2. Faulty or damaged control module connected to Bus E (ECM, BCM, TCM, etc.)
3. Poor or corroded ground connections affecting the network
4. Incorrectly installed aftermarket devices (alarms, remote start, audio)
5. Water ingress or moisture in connectors or junction boxes
6. Internal wiring failure inside harness connectors

Step-by-Step Diagnostic Process for U0071 #

Careful diagnosis is key to resolving U0071 efficiently. Rushing to replace modules without checking the wiring can lead to unnecessary costs and frustration. Here’s a systematic approach:

• Retrieve all stored and pending codes using a professional scan tool. Note any module communication errors.
• Visually inspect the VAN Data Bus E (-) wiring for obvious damage, burn marks, or pinched sections.
• Check all network-related connectors for corrosion, moisture, or bent pins.
• Measure voltage on the VAN Bus E (-) line with the ignition on. Normal voltage should be around 0–2V; anything significantly higher indicates a short to power.
• Isolate modules on the Bus E by disconnecting them one at a time (following OEM safety procedures) to see if the voltage drops to normal. The faulty module will cause the voltage to remain high when connected, and normalize when disconnected.
• Inspect ground points for all affected modules. Clean and tighten as needed.
• If aftermarket accessories are present, temporarily disconnect them to check for interference with the data line.
• Refer to OEM wiring diagrams to trace the affected circuit and verify continuity/resistance as specified.

Potential Repairs for U0071 #

Once the root cause of the U0071 code is identified, repairs will depend on the specific issue uncovered during the diagnostic process. Here are the most common solutions:

• Repair or replace damaged, shorted, or corroded VAN Data Bus E (-) wiring
• Replace the faulty control module responsible for the high voltage
• Clean or repair ground connections for affected modules
• Remove or properly integrate aftermarket electronics interfering with the data bus
• Seal connectors, junction boxes, or harnesses against moisture ingress
• Replace faulty connector pins or repair harness connectors as needed

Is It Safe to Drive With Code U0071? #

Limited—Driving with U0071 is generally not recommended. While the vehicle may still operate, the risk of losing critical functions—like ABS, stability control, or power steering—can compromise safety. In some cases, the vehicle may enter limp mode or even fail to start. If you notice pronounced electrical issues or warning lights, it’s best to have the vehicle inspected and repaired as soon as possible.

Vehicles Most Commonly Affected by U0071 #

While U0071 is a generic OBD-II code, it’s more frequently encountered in vehicles from manufacturers that use extensive networking for module communication. Based on field experience, the following makes and models are often affected:

• Renault (Clio, Megane, Scenic with VAN bus architecture)
• Peugeot and Citroën (PSA group vehicles from the 2000s–2010s)
• Honda (various Accord and Civic models)
• General Motors (Chevrolet, GMC, Opel with advanced body networks)
• Toyota (specific models with CAN/VAN hybrid networks)
• Ford (Focus, Fiesta, Fusion with multiple communication buses)

Common Mistakes & Best Practices for U0071 #

Misdiagnosis is common with U0071, often leading to unnecessary replacement of expensive modules. The network nature of the code means a single wiring or grounding issue can mimic a module failure. Here are some frequent errors and how to avoid them:

• Replacing control modules before checking wiring and grounds
• Overlooking aftermarket accessories as possible sources of interference
• Ignoring connector corrosion or water damage, especially in humid or flood-prone areas
• Failing to use OEM wiring diagrams for accurate diagnostics
• Not clearing codes and rechecking after repairs to confirm resolution

Quick FAQ for U0071 #

Is U0071 a serious code?
Yes, it can be. Any issue with the vehicle’s communication network can affect multiple safety and drivability systems. Immediate diagnosis is recommended.

Can I clear the U0071 code and keep driving?
Clearing the code without fixing the root cause will only make it disappear temporarily. The underlying network issue may return at any moment—often with more severe symptoms.