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U0038 — Vehicle Communication Bus B Performance

Generic OBD-II · all makesNetwork / communication

Code U0038 indicates that the vehicle's communication network (Bus B) is experiencing performance issues. This means that while the network is functioning, the data being transmitted is intermittent, delayed, or corrupted.

Symptoms

What causes it — most likely first

1. Wiring Harness Damage

Chafed, pinched, or corroded wires on the CAN Bus B network causing signal interference.

2. Faulty Network Module

A malfunctioning module connected to Bus B sending 'noise' or invalid data onto the network.

3. Corroded Connectors

Moisture or oxidation at connector pins increasing resistance and disrupting signal integrity.

4. Low System Voltage

A failing battery or alternator causing modules to operate below the required voltage threshold.

5. Control Module Failure

Internal hardware failure within the PCM or ECM disrupting network management.

How it's diagnosed

  1. Verify battery voltage and ensure the charging system is operating within specifications.
  2. Inspect the Bus B wiring harness for visible signs of wear, melting, or corrosion.
  3. Measure resistance across the CAN high and CAN low lines to check for shorts or opens.
  4. Disconnect suspected modules on Bus B one by one to see if communication stability returns.
  5. Use an oscilloscope to analyze the signal waveform for noise or voltage drops.

Code facts & related codes

SystemNetwork / communication
StandardizationSAE generic — identical on every make

Frequently asked

Does this code mean I need a new engine computer?

Rarely. While the PCM is part of the network, U0038 is most often caused by wiring faults or a failing peripheral module rather than the PCM itself.

Can a bad ground cause a communication bus error?

Yes, poor grounding can create electrical noise that interferes with the high-speed data signals on the communication bus.

Is it safe to drive with this code?

It depends on which systems are affected; if critical safety systems like ABS or airbags are malfunctioning, the vehicle may be unsafe.