U2338 — UBP communication bus fault

U2338 is stored when the ECU sees malfunction on the circuit named in the code. That describes how the circuit is behaving, not which part has failed — the wiring, the connector and the component itself can all produce it, which is why the checks below start with the cheapest.

Common causes

The cause is almost always one of a few things. Here they are — U2338 rarely comes from anything outside this list:

• Wiring or connector fault in the circuit
• Component failed electrically
• Supply or ground problem feeding the circuit
• Controlling module fault, though this is the least common of the four

Where to start

In the order a sensible mechanic would work — the cheap checks first, the expensive replacements only after:

1. Read all stored codes — a general fault code is often the symptom of a more specific one
2. Inspect the connector and wiring for the named component
3. Check supply and ground at the component
4. Measure the component against specification
5. Replace the component once wiring and supply are ruled out

That is what holds for U2338 in general. From here it depends on your engine — tell me which car it is and what it does, and I will give you the steps for it: real procedures, torque figures and diagrams instead of general advice.