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U0005 — High Speed Can Communication Bus High

Generic OBD-II · all makesNetwork / communication

The U0005 diagnostic code indicates that the Engine Control Module (PCM) has detected a high voltage condition on the High-Speed CAN communication bus's High circuit. This means the CAN-H wire is shorted to power or has lost its proper termination, preventing the vehicle's control modules from exchanging data reliably.

Symptoms

What causes it — most likely first

1. Wiring shorted to power

The CAN-H circuit wiring is chafed or damaged, causing it to short to a constant power source like the battery or ignition circuit.

2. Failed CAN bus terminating resistor

An internal short or failure in one of the CAN network's terminating resistors alters the bus voltage and disrupts communication.

3. Internal module short

An internal electrical short inside a module connected to the CAN bus pulls the High circuit voltage up.

4. Corroded or damaged connector

Corrosion or bent pins in a CAN bus connector bridge the High circuit to an adjacent power circuit.

5. PCM/ECM failure

An internal fault within the Engine Control Module causing it to incorrectly read or pull up the bus voltage, which is extremely rare.

How it's diagnosed

  1. Use an OBD-II scanner to check for all network codes and identify which modules are failing to communicate.
  2. Visually inspect the wiring harness and connectors for the CAN bus, focusing on areas subject to chafing, heat, or moisture.
  3. Disconnect modules on the network one by one to see if the high voltage condition clears, isolating a shorted module.
  4. Measure the resistance between the CAN-H and CAN-L pins at the DLC; it should read approximately 60 ohms with the ignition off.
  5. Use a digital multimeter to check for power (battery voltage) on the CAN-H wire, confirming a short to power.
  6. If all wiring, resistors, and connected modules test normally but the fault persists, suspect the PCM as a last resort.

Code facts & related codes

SystemNetwork / communication
StandardizationSAE generic — identical on every make
Related codesU0001 — High Speed Can Communication BusU0002 — High Speed Can Communication Bus PerfoU0003 — High Speed Can Communication Bus OpenU0004 — High Speed Can Communication Bus LowU0006 — High Speed Can Communication Bus OpeU0007 — High Speed Can Communication Bus Low

Frequently asked

Does the U0005 code mean my Engine Computer (PCM) is bad and needs replacement?

No, it almost never does. While a failed PCM is possible, it is extremely rare. Drivers are frequently told to replace the PCM for this code, but the actual cause is almost always a wiring issue, a shorted terminating resistor, or a fault in a different module on the network.

Can I still drive my vehicle with a U0005 code?

It is generally not recommended. Because the High-Speed CAN bus is critical for major vehicle operations, a fault here can cause unpredictable behavior, stalling, or the loss of safety-critical functions like stability control.

What is the most common cause of a high voltage condition on the CAN bus High circuit?

The most common cause is physical wiring damage where the CAN-H wire has chafed against the vehicle body or another wire and shorted directly to a power source.

How do you test the CAN bus terminating resistors?

With the ignition off and the battery disconnected, measure the resistance between pins 6 (CAN-High) and 14 (CAN-Low) at the OBD diagnostic port. A normal reading is around 60 ohms; a reading of 120 ohms indicates one resistor is open, and a reading near 0 ohms indicates a short.