U0017 — Controller Area Network (CAN) Data Bus: Medium Speed Bus(-) – Voltage High #

Note: The wording of this code may differ depending on the vehicle manufacturer (OEM).

• CAN Data Bus Medium Speed Circuit High (Ford)
• CAN Communication Line – High Voltage (GM/Chevrolet)
• CAN Bus Medium (-): High Voltage (Toyota)
• Medium Speed CAN Bus(-) Circuit High (Honda/Acura)

Summary of Code U0017 #

DTC U0017 indicates an issue detected by the vehicle’s onboard computer with the medium-speed Controller Area Network (CAN) data bus, specifically that the voltage on the negative (-) bus line is higher than expected. The CAN bus is the digital backbone for communication between various control modules—such as the engine, transmission, or body control module. When there is a voltage anomaly on this network, some modules may not be able to “talk” to each other properly, leading to erratic behavior or loss of certain functions. This code doesn’t point to a specific module, but rather to the communication line itself. U0017 often requires methodical electrical troubleshooting to pinpoint the root cause.

Frequent Symptoms for Code U0017 #

The symptoms for a U0017 CAN bus voltage high issue can be mild or severe, depending on which modules or systems are affected. Sometimes, the car may appear to run normally, but in other cases, you might experience a cascade of electrical gremlins. Here are some of the most common signs:

• Warning lights on the dashboard (ABS, traction control, check engine, etc.)
• Loss of communication with one or more modules (engine, transmission, body, etc.)
• Intermittent electrical issues—windows, locks, or other accessories not working properly
• Failure of certain systems to operate (e.g., power steering, infotainment, HVAC)
• Hard starting or stalling, in rare cases
• No communication with scan tools on the diagnostic port

Probable Causes for Code U0017 (by Frequency) #

Most CAN bus faults come down to wiring issues, but other possible roots include module failure or aftermarket modifications. Here’s what technicians most commonly find, listed by likelihood:

1. Wiring damage or corrosion—especially at connectors or splices in the CAN medium-speed circuit
2. Poor or loose ground connections affecting the CAN network or control modules
3. Faulty control module (rare, but possible if a module is internally shorted or pulling up the bus voltage)
4. Aftermarket accessories tapped into the CAN wires (alarms, remote starters, radios)
5. Water intrusion in harnesses or module housings
6. Short to power in the CAN (-) wire (e.g., insulation damage contacting a 12V line)

Step-by-Step Diagnostic Guide for U0017 #

A correct diagnosis requires patience and a systematic approach. The goal is to locate where the CAN (-) line is seeing an abnormally high voltage. Here’s a proven workflow:

• 1. Verify the code: Scan all modules for U-codes, record any related codes, and clear them. See if U0017 returns quickly or only after driving.
• 2. Visual inspection: Examine wiring harnesses, connectors, and grounds—especially areas exposed to moisture or abrasion. Look for greenish corrosion, pinched wires, or evidence of rodent damage.
• 3. Check aftermarket devices: Remove or disconnect any non-OEM electronics spliced into CAN wiring. Re-test for code.
• 4. Measure CAN line voltage: With the ignition on, backprobe the CAN (-) wire at the DLC (diagnostic link connector) and compare to specification (usually around 2.5V). Anything over 3V is suspect.
• 5. Isolate harness sections: Disconnect modules or harness junctions one at a time to see if voltage normalizes, helping identify the affected branch or module.
• 6. Test continuity and shorts: Use a multimeter to check for shorts to power or ground between CAN (-) and other wires. Repair as needed.
• 7. Replace suspect module last: Only after eliminating wiring/connector causes, consider swapping in a known-good module (if possible).

Possible Repairs for U0017 #

The repair depends on what the diagnostics reveal, but most fixes fall into these categories:

• Repair or replace damaged wiring—splice in new wire, repair insulation, or replace connectors as needed
• Clean and secure grounds at all module and chassis points related to CAN
• Remove or rewire aftermarket devices to avoid interference with CAN circuits
• Replace faulty module if it is proven to be internally shorted or causing high voltage
• Seal areas prone to water intrusion and dry out harnesses

Can You Drive With Code U0017? #

Limited—exercise caution. In many cases, the vehicle will start and drive, but safety or convenience features may be lost. If you notice major warning lights (ABS, traction, airbag), or if the car enters limp mode, it’s safest to have it towed. Prolonged driving with a CAN bus fault can sometimes cause further module communication errors or even battery drain. Always address U0017 promptly.

Vehicles Most Commonly Affected by U0017 #

This code is most often reported on vehicles that use medium-speed CAN networks for body and convenience modules. These include, but are not limited to:

• Ford (Fusion, Escape, F-series trucks, Edge)
• GM/Chevrolet (Malibu, Silverado, Equinox)
• Toyota (Camry, RAV4, Tacoma)
• Honda/Acura (Civic, Accord, CR-V, MDX)
• Volkswagen (Passat, Jetta, Tiguan)
• Chrysler/Jeep/Dodge (Grand Cherokee, Pacifica, Ram 1500)

Common Mistakes & Best Practices for U0017 #

Technicians and DIYers sometimes make these missteps when chasing CAN bus faults. Here’s how to avoid them:

• Replacing modules before checking wiring—wiring faults are far more common than failed modules
• Missing hidden aftermarket devices (e.g. remote starters, GPS trackers) that tap into CAN lines
• Overlooking water damage or corrosion in out-of-sight connectors (A-pillar, under carpet, kick panels)
• Failing to verify proper ground integrity for all affected modules
• Not using proper backprobe techniques—never pierce insulation unless absolutely necessary

Quick FAQ for Code U0017 #

Q: Can a weak battery or alternator cause U0017?
A: Rarely. While low voltage can trigger some communication codes, U0017 specifically points to a high voltage condition on the CAN (-) circuit, usually caused by wiring or module faults.

Q: Does a U0017 code mean a major repair is needed?
A: Not always. Many U0017 cases are resolved with simple wiring repairs or by undoing an improper aftermarket install. Module replacement is only rarely necessary.