AutoCodes - OBDII Code List - U0004
U0004 - High Speed CAN Communication Bus (+) Low
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U0004 Possible Causes
- Diagnosis of this Diagnostic Trouble Code (DTC) is accomplished via the vehicle symptom(s)
- Check for more codes
- Faulty Control Module
- Control Module harness is open or shorted
- Control Module circuit poor electrical connection
How do I fix code U0004?
Check the "Possible Causes" listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector's pins.
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Cost of diagnosing the U0004 code
Labor: 1.0
The cost of diagnosing the U0004 code is 1.0 hour of labor. The auto repair labor rates vary by location, your vehicle's make and model, and even your engine type. Most auto repairs shops charge between $75 and $150 per hour.Possible Symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
U0004 Description
A Controller Area Network (CAN) is a vehicle bus standard designed to interconnect automotive devices without a host computer. Operating information and commands are exchanged among the devices. The devices have programmed information about what messages are needed to be exchanged on the serial data circuits. CAN bus uses two dedicated wires for communication. The wires are called CAN high and CAN low. When the CAN bus is in idle mode, both lines carry 2.5V. When data bits are being transmitted, the CAN high line goes to 3.75V, and the CAN low drops to 1.25V, thereby generating a 2.5V differential between the lines. Since communication relies on a voltage differential between the two bus lines, the CAN bus is NOT sensitive to inductive spikes, electrical fields, or other noise. The Diagnostic Trouble Code (DTC) sets when a supervised periodic message that includes the transmitter device availability has not been received.
More Information
Need more information on how to fix the U0004 code?Get Access to Factory Service Manuals
Information for specific makes
- U0004 FORD High Speed CAN Communication Bus (+) Low
- U0004 LINCOLN High Speed CAN Communication Bus (+) Low
- U0004 MERCURY High Speed CAN Communication Bus (+) Low
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