U0026Generic code

U0026 Code: Low Speed CAN Communication Bus (-) High

The U0026 code means the computer detected a high voltage, a short to positive, on the low speed CAN bus (-) wire. It usually sets communication codes in several modules and, depending on the network affected, limp mode or a dash full of warning lights. A wire stuck at positive stops communication on the whole network.

Severity
High
Can I keep driving?
Yes, but with caution
Estimated cost
$0 to $1,500
Difficulty
Hard
System
Communication Network
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the U0026 code means

A CAN network uses two twisted wires: CAN high (+) and CAN low (-). At rest both sit near 2.5 V. When a module transmits, the high wire rises toward 3.5 V and the low wire drops toward 1.5 V. There is a 120 ohm termination resistor at each end of the network, and the two in parallel add up to 60 ohms.

The U0026 code means the computer detected a high voltage, a short to positive, on the low speed CAN bus (-) wire. A wire stuck at positive stops communication on the whole network.

The high speed network usually ties together the engine, transmission, ABS and steering modules, while the medium or low speed network serves the comfort modules (body, doors, climate control, radio). Knowing which modules are affected points you toward where to look.

Work the diagnosis in this order: 1) battery and alternator, because low system voltage is the number one cause of bursts of U codes; 2) the module list on the scan tool, to see which module is not responding; 3) power, fuses and grounds of the module that is not responding; 4) network resistance at the OBD2 connector, about 60 ohms between pins 6 and 14 with the battery disconnected; 5) connectors and wiring at the module, especially in areas exposed to moisture such as under the carpets, in the doors and in the trunk.

Measuring the network and isolating the module that is bringing it down is the heart of any U code diagnosis, so take the time to do those steps in order before you replace anything.

U0026 code symptoms

  • Many warning lights on at the same time.
  • Several U codes stored in different modules.
  • Limp mode, or an engine that will not start (high speed network).
  • Comfort functions that do not respond (low speed network).

Likely causes of the U0026 code

  1. Damaged network wiring: cut, chafed or soaked with moisture.
  2. A shorted module that drags the network down: you find it by unplugging modules one at a time.
  3. Missing or damaged termination resistor: the total resistance goes from 60 to 120 ohms.
  4. Connectors with water or corrosion: check the locking tab, the pins and any sign of moisture or corrosion.
  5. An accessory plugged into the network: alarms, trackers and OBD2 adapters.
  6. Weak battery: it causes communication errors.

How to diagnose the U0026 code step by step

  1. Measure the resistance between OBD2 pins 6 and 14 with the battery disconnected. You should see about 60 ohms. A reading of 120 means a termination resistor is missing or a section of the network is open, and a reading near 0 means the two wires are shorted together.
  2. Measure the voltage on each wire with the key on. CAN high should read 2.5 to 3.5 V and CAN low 1.5 to 2.5 V. A reading of 0 V or 12 V points to a short.
  3. Unplug the modules one at a time until the network starts working again.
  4. Inspect the wiring in areas where it rubs or gets wet.
  5. Remove any accessories connected to the network.

How to fix the U0026 code

  • Repair the wiring and keep the twist in the wires.
  • Replace the module that is bringing the network down.
  • Remove poorly installed accessories.
  • Clear the codes in all modules.

Technical reference data

  • Resistance between pins 6 and 14: about 60 ohms.
  • Terminations: 120 ohms each.
  • CAN high: 2.5 to 3.5 V. CAN low: 1.5 to 2.5 V.
  • These values are a guide only, so check the manufacturer data for your vehicle.

Brand-specific notes

After you fix the U0026 code, clear the codes in all modules. Many of them keep old U codes from the time the fault was present. Accessories installed after the sale, such as alarms, GPS trackers and OBD2 adapters left plugged in permanently, are a frequent cause of network problems.

Frequently asked questions about U0026

Can I drive with a U0026 code?
With caution. Important systems can fail, so keep trips short until the network is checked.
Why are so many warning lights on?
Because the modules cannot exchange information with each other, each one reports a communication fault.
How do I find the fault?
Measure the network at the OBD2 connector and unplug the modules one at a time.
How much does it cost to fix U0026?
Anywhere from $0 to $1,500 depending on the cause. A loose connector costs nothing, while a failed module is at the top of that range.
What does the U0026 code mean?
It is a generic OBD2 code that means the low speed CAN bus (-) wire has a high voltage, a short to positive. The modules on that network cannot talk to each other.
Will a U0026 code clear itself?
Only if the short was temporary, such as a wet connector that dried out. If the fault is still there, the code comes right back.
What is the most common cause of U0026?
Damaged wiring or a connector with moisture or corrosion. A weak battery and accessories plugged into the network are the next things to rule out.

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