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DTC codes / U00xx · Network wiring and bus faults / U0098

U0098Vehicle Communication Bus H (-) Low

U0098 indicates that the vehicle's communication bus H (-) circuit is reading low voltage, meaning the controller area network (CAN) high-speed negative line is shorted to ground or otherwise pulled below its normal operating range. The powertrain control module (PCM) or another module on that bus has detected the abnormal voltage and stored this code, often disabling communication with other modules.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaNetwork wiring and bus faults

Symptoms you may notice

  • Multiple warning lights illuminated on the dashboard, including the check engine light, ABS, and airbag lights
  • The engine may start and run normally, or it may crank but not start if the bus is completely down
  • Intermittent or complete loss of communication with scan tools and other diagnostic equipment
  • Erratic operation of electronic features such as the radio, power windows, or instrument cluster
  • No symptoms besides the warning light when the fault is intermittent or only affects non-critical modules

Common causes, most likely first

  1. A short to ground in the CAN bus H (-) wire, often due to chafed insulation or a pinched harness
  2. A faulty module on the bus that is internally shorting the H (-) line to ground
  3. Corroded or damaged connector pins at any module or inline harness connector on the bus
  4. Water intrusion into a connector or module causing a conductive path to ground
  5. Aftermarket electronics improperly tapped into the bus wiring, creating a low-resistance path
  6. A failed terminating resistor inside a module, altering bus voltage levels
  7. A broken or loose ground connection for a module, causing the bus reference voltage to drop

How to diagnose and fix it

  1. Connect a scan tool and check for communication with all modules to identify which modules are offline and narrow down the bus segment
  2. Measure resistance between CAN H (-) and ground with the battery disconnected; a reading well below 60 ohms suggests a short to ground
  3. Visually inspect the harness along its routing for chafing, pinches, or damage, especially near sharp edges and moving components
  4. Disconnect modules one at a time and recheck bus voltage to isolate a module that is internally shorting the line
  5. Check for water intrusion or corrosion at connectors and modules, cleaning or replacing as needed
  6. Repair or replace the damaged section of harness, ensuring proper routing and protection
  7. Clear the code and verify communication is restored across all modules with a scan tool

Hidden causes of a low CAN bus H line

  • A common oversight is blaming the PCM first, but the fault often lies in a non-critical module such as a door control unit or seat memory module that is shorting the bus.
  • Aftermarket accessories like remote starters or alarm systems are frequently tapped into the CAN bus and can introduce a short to ground that only appears when the accessory is active.
  • The CAN H (-) line is part of a differential pair; a short to ground on this line can sometimes be caused by a short to the CAN L (+) line, so check for cross-shorts between the two wires.
  • Intermittent U0098 codes often set when the vehicle is driven over rough roads, indicating a loose connector or a harness that rubs only under vibration.
  • A low battery or charging system fault can cause modules to drop offline and set communication codes, so always verify battery voltage and ground integrity before chasing the bus wiring.

Can I keep driving with U0098?

If the engine starts and runs normally and only the warning light is on, you can drive the vehicle to a repair shop, but avoid long trips and be aware that other electronic systems may malfunction. If the engine does not start or multiple safety systems are disabled, do not drive and have the vehicle towed.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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