High Speed CAN Communication Bus (-) High
What it means
U0008 means the voltage on the high-speed CAN low wire (bus -) is reading too high, disrupting communication on the network that ties the vehicle's modules together. Because many modules share this bus, the effects vary — warning lights, dropped modules, erratic gauges, and in some cases limp mode or a no-start. The cause is usually a short to voltage, damaged bus wiring, or a failed module dragging the bus.
Can I keep driving? Sometimes limited — a fault on the high-speed bus can knock out multiple modules, causing warning lights, limp mode, or in some cases a no-start, so diagnose it before relying on the vehicle.
Common symptoms
What you'll notice
- Check-engine light plus multiple warning lights
- Several modules unresponsive or dropping out (many U-codes stored)
- Erratic gauges/instrument cluster
- Possible limp mode, stalling, or no-start depending on which modules are affected
Common causes
Most likely first
- Short to voltage on the CAN low (bus -) wireLikely
- Damaged, chafed, or corroded CAN bus wiring/connectorCommon
- A failed module pulling the bus voltage highCommon
- Failed CAN terminating resistorLess often
- Water intrusion into a bus connectorLess often
How to diagnose & fix
Work through it in order
- Scan all modules and note every stored U-code to map which are affected.
- Inspect the high-speed CAN wiring and connectors for damage, chafing, or a short to power.
- Measure bus resistance across CAN-H/CAN-L (about 60 ohms with two terminators) with the key off.
- Disconnect modules one at a time to find one dragging the bus voltage.
- Repair the wiring or replace the faulty module/terminating resistor, then clear and re-test.
FAQ
Quick answers
Is it safe to drive with U0008?+
Can I just clear U0008?+
Related codes
Often seen with U0008
Read & clear U0008 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.