What it means
A control module detects voltage below the expected level on the negative conductor of vehicle communication bus E. It sets the code when the bus line remains below its calibrated voltage threshold.
How it works
Bus E sends messages between connected control modules over positive and negative conductors. U0070 means the monitored voltage on the Bus E negative conductor is below its expected range, which may interfere with communication on that network.
Common causes
Most likely first.
- Short to ground on bus wire
- Damaged or chafed wiring
- Poor connector connection
- Faulty module pulling the bus low
- Low system voltage
Symptoms
- Communication warning lights
- Multiple warning messages
- Intermittent system operation
- Some systems unavailable
How to diagnose it
- Scan all modules and record freeze-frame data and communication faults to determine whether the low-line event affected several Bus E devices.
- Check battery voltage and charging condition, then inspect Bus E negative wiring and connectors for chafing, corrosion, loose terminals, or contact with ground.
- With power isolated as specified by the manufacturer, test the Bus E negative conductor for an unintended short to ground and inspect suspect sections for damage.
- Measure the negative-line signal and bus termination resistance at manufacturer-specified points, comparing each result with the manufacturer's specification.
- If wiring and termination are sound, isolate Bus E modules one at a time using the manufacturer's procedure to find a module pulling the negative conductor low.
Common fixes
- Repair chafed Bus E negative wiring or correct an unintended ground connection.
- Clean, secure, or replace a poor connector or terminal.
- Correct low system voltage by repairing the battery or charging-system fault identified by testing.
- Repair or replace a Bus E module that tests as pulling the negative conductor low.
Can I keep driving?
If communication warnings are accompanied by unreliable steering, braking, powertrain, or other essential functions, stop driving when safe and arrange repair. Otherwise, limit driving because intermittent Bus E faults can make connected systems unavailable.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.