U0005 – High Speed CAN Communication Bus (+) High

Last updated: April 7, 2026

U0005 means the vehicle detected a network problem that can make modules drop offline and cause multiple warning lights or odd electrical behavior. You may notice a no-start, a dead dash, or features that stop working without warning. The official definition is “High Speed CAN Communication Bus (+) High,” which points to the CAN bus “plus” line reading higher than expected. According to some manufacturers’ factory diagnostic data, U0005 sets when a module decides the High Speed CAN Bus (+) signal stays biased high long enough to disrupt communication. The code does not name a failed module. Diagnosis must identify which module, splice, or harness section caused the bus to go high.

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U0005 Quick Answer

U0005 points to the High Speed CAN Bus (+) line being pulled high and disrupting communication. Start by checking which modules won’t communicate, then inspect CAN wiring/connectors and module power/grounds before replacing anything.

What Does U0005 Mean?

U0005 code means a control module logged “High Speed CAN Communication Bus (+) High.” In plain terms, the car’s main communication network acted like it got stuck in the wrong electrical state. When that happens, modules can’t reliably share data. The result can range from a warning light to a no-start, depending on which modules drop out.

Technically, the module monitors High Speed CAN Bus (+) voltage behavior and message validity. It expects CAN (+) and CAN (–) to toggle as data moves. U0005 sets when the CAN (+) circuit appears biased too high and communication fails. SAE J2012 U-codes stay intentionally general. The code only points you toward the network condition, not a confirmed bad module.

Theory of Operation

High Speed CAN is a two-wire, twisted-pair network that links the ECM/PCM, ABS, TCM, BCM, and other modules. The pair uses CAN (+) and CAN (–) to carry differential signals. Each module transmits messages and listens for others. Termination and correct bias keep the network stable and resistant to noise.

U0005 occurs when something forces CAN (+) higher than the network can tolerate. A short to B+, water in a connector, or a module internal driver fault can hold CAN (+) high. A poor module ground can also shift the bias and distort the signal. Once the bus loses its normal differential swing, modules miss messages and start logging U-codes. One failing node can take down the whole bus.

Symptoms

U0005 symptoms usually show up first as scan tool communication problems, then as multiple system warnings.

• Scan tool dropouts: One or more modules show “no communication” or appear and disappear during a network scan.
• Multiple warning lights: ABS, traction control, airbag, and MIL may illuminate together after the bus fault.
• No-start or crank/no-start: The ECM may not receive immobilizer, PRNDL, or key status messages.
• Dead or flickering cluster: The instrument panel may reset, freeze, or lose gauge data due to missing CAN messages.
• Intermittent shifting issues: The transmission may default to limp mode if the TCM loses network data.
• Loss of driver assists: Power steering assist, stability control, or ADAS features may disable when the bus goes down.
• Battery drain: A bus stuck in an abnormal state can keep modules awake and increase key-off draw.

Common Causes

• CAN (+) (CAN High) shorted to battery voltage: A pinch, rub-through, or incorrect splice can drive CAN (+) above its normal bias and trigger the “bus (+) high” detection.
• Water intrusion or corrosion in a CAN connector: Moisture bridges terminals and raises circuit voltage, which can hold CAN (+) high and destabilize network messaging.
• High resistance in CAN (+) due to damaged strands: Partially broken wire strands can distort the waveform and bias, making the module interpret the CAN (+) line as stuck high.
• Aftermarket accessory or remote start tied into the CAN wiring: Poorly integrated modules can backfeed voltage or load the bus, which can force CAN (+) high during certain key states.
• Short between CAN (+) and another powered circuit in the harness: A loom contact with ignition feed, sensor reference, or lighting power can elevate CAN (+) and set U0005.
• Module internal fault pulling CAN (+) high: A failed transceiver inside any controller on the HS-CAN can bias the bus high and interrupt communication across multiple modules.
• Terminating resistor / network topology fault: Incorrect termination or a wiring change can alter bus loading and bias, which can contribute to a “stuck high” interpretation on CAN (+).
• Poor module power/ground creating false bus readings: A controller with a weak ground or supply can misread bus voltage and set U0005 even when the wiring looks intact.

Diagnosis Steps

Tools you need include a scan tool with a full network scan, a DVOM with min/max, and basic back-probing leads. Use wiring diagrams to identify HS-CAN (+) and HS-CAN (−), splice packs, and termination points. Have a battery charger available. Network faults often appear during crank and low voltage events.

1. Confirm U0005 on a full scan. Record whether it shows as pending or confirmed/stored, and note which module reported it. Save freeze frame data for ignition state, vehicle speed, system voltage, and any related U-codes. Freeze frame shows conditions when the DTC set.
2. Run a network scan and document which modules do not report. This step matters for U0005 because a missing module can point to the harness leg that drives CAN (+) high. If the scan tool cannot communicate with multiple modules, treat it as a bus-level issue first.
3. Check fuses and power distribution for the modules that are offline or reporting U0005. Verify battery voltage and key power feeds at the fuse block. Do this before probing at any controller connectors.
4. Voltage-drop test module power and ground under load. Turn the ignition ON and command loads when possible. Measure ground drop from module ground pin to battery negative while the module operates, and keep it under 0.1V. A weak ground can mimic communication faults.
5. Inspect the HS-CAN harness and connectors in high-risk areas. Focus on kick panels, under- runs, firewall pass-throughs, and any recent repair zones. Look for crushed loom, green corrosion, spread terminals, and evidence of water intrusion.
6. Identify any aftermarket devices that tie into CAN. Unplug them temporarily and recheck network communication. Many U0005 cases trace back to backfeeding voltage onto CAN (+) through an accessory module.
7. With ignition OFF and the battery disconnected, measure HS-CAN resistance between CAN (+) and CAN (−) at an accessible module connector or DLC when applicable. A healthy bus reads about 60 ohms because two 120-ohm terminators sit in parallel. Readings near 120 ohms or OL suggest an open or missing termination that changes bus behavior.
8. Reconnect the battery and turn ignition ON. Measure CAN (+) and CAN (−) to ground with the DVOM. Bias voltage only exists with the circuit powered, so ignition-OFF readings do not help. A healthy HS-CAN typically sits near 2.5V on both lines; if CAN (+) stays abnormally high, suspect a short to power or a module pulling it up.
9. Isolate the fault by unplugging modules one at a time on the affected bus segment. Watch CAN (+) voltage and module presence on the network scan after each disconnect. When the voltage returns to normal and communication resumes, the last disconnected branch contains the fault.
10. Once you narrow the branch, inspect that leg for a CAN (+) short to power. Use a fused jumper, wiggle testing, and continuity-to-power checks with the battery disconnected. Repair wiring faults with proper splices and shielding practices, then reroute to prevent future rub-through.
11. Clear codes and perform a verification drive. Use a scan tool snapshot to capture live network status during the same conditions seen in freeze frame. Snapshot helps catch intermittent spikes that freeze frame cannot show again. Confirm no U0005 returns as pending or confirmed after multiple key cycles.

Professional tip: When U0005 sets during crank, focus on voltage drop and power distribution first. A module that browns out can “see” CAN (+) high and log the code. Fixing a weak ground or battery cable can restore stable bus bias without touching CAN wiring.

Possible Fixes

• Repair CAN (+) short-to-power wiring damage: Locate the rub-through or pinch point, then repair with correct splicing and loom protection to prevent recurrence.
• Clean and restore corroded network connectors: Remove corrosion, correct terminal tension issues, and address the water entry path that raised CAN (+) voltage.
• Remove or rework aftermarket CAN integrations: Disconnect the device for confirmation, then rewire using an approved interface that does not backfeed the bus.
• Restore module power/ground integrity: Repair high-resistance grounds, loose power feeds, or damaged fuse block connections found during voltage-drop testing.
• Replace a confirmed bus-disturbing module: If disconnect testing proves one controller pulls CAN (+) high, replace or reprogram it per OEM procedures after verifying wiring integrity.
• Correct termination or network topology faults: Repair missing terminators, damaged splice packs, or incorrect harness repairs that altered bus resistance and bias.

Can I Still Drive With U0005?

You can sometimes drive with a U0005 code, but you should treat it as a risk until you confirm what dropped off the network. U0005 means a module saw the High Speed CAN Bus (+) line biased high. That can stop modules from exchanging messages. In the real world, that can disable systems that depend on network data. Expect warning lights, lost scan tool communication, and features that quit without notice. If the engine runs normally and steering and brakes feel normal, you may limp it to a shop. Avoid long trips, high speeds, and heavy traffic. Stop driving if you lose the speedometer, get multiple warning lights at once, experience hard shifting, or the vehicle stalls. A bus fault can spread quickly as more modules time out.

How Serious Is This Code?

U0005 ranges from an inconvenience to a no-start, depending on which modules need high-speed CAN data. In mild cases, you see a MIL and some stored U-codes, yet the vehicle drives fine. In severe cases, the CAN bus gets “stuck” and several modules go offline. That can trigger limp mode, harsh shifts, dead gauges, or an intermittent stall. Safety risk depends on what drops out. ABS, traction control, stability control, power steering assist, and electronic brake functions may disable if they cannot validate network messages. You should also take the code seriously because a CAN (+) high condition often comes from wiring damage or moisture intrusion. Those faults can worsen and create collateral issues in connectors and splices.

Common Misdiagnoses

Techs often blame the last module that “won’t talk” and replace it first. That mistake costs money and rarely fixes U0005. A CAN (+) high fault usually comes from the network, not a single module. Another common miss involves skipping power and ground checks to the “silent” module. A module with a weak ground can load the bus and mimic a network failure. Many also ignore aftermarket devices. Remote starts, alarms, GPS trackers, and radio upgrades frequently tie into CAN wiring and pull CAN (+) high. Finally, some clear codes and road test once, then call it fixed. Intermittent bus faults need a repeatable reproduction method and a recheck for pending codes and returning communication dropouts.

Most Likely Fix

The most common U0005 repair direction is restoring CAN bus wiring integrity at known failure points. Focus on rubbed-through harnesses, water intrusion at connectors, and corroded splice packs on the High Speed CAN Bus (+) circuit. A close second involves correcting a module power or ground fault that biases the bus high under load. After repairs, confirm the fix by running a network scan multiple times and driving under the same conditions that set the code. Enable criteria vary by vehicle, so use service information to match the original failure conditions before you declare the U0005 repair complete.

Repair Costs

Network and communication fault repairs vary by root cause — wiring/connectors are often the source, but module-level repairs or replacements can be significantly more expensive.