U0070
Communication Bus "B" Performance
The secondary communication bus (Bus B, often a chassis or comfort sub-bus) shows reduced performance — high error rate, intermittent dropouts, or framing errors. Bus is still alive but unreliable.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: hard
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Common causes
Ordered by how often each turns out to be the cause.
- Marginal wiring or corroded connectorCommon
- EMI interference (aftermarket equipment)Possible
- Gateway module routing CAN messages incorrectlyLess likely
Parts involved
- CAN Bus Wiring
- CAN Terminating Resistor
U0070 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.