U0104 Code: Lost Communication with Cruise Control Module

What the U0104 code means

The modules in the vehicle exchange information constantly over the data network, normally CAN. The cruise control module manages cruise control and, on some vehicles, adaptive cruise control. When the other modules stop receiving its messages for a while, they log the U0104 code.

The code is stored by the module that misses the information, not by the one that is failing. That is why it often shows up in several modules at once. The problem can be in the cruise control module itself (no power, no ground or failed), in its connector or in the network wiring that reaches it.

Usual location: behind the front bumper (the radar) or under the dash. If that area is exposed to water or was recently repaired, start there.

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.

U0104 code symptoms

• Warning lights on the dash.
• Cruise control does not work.
• Communication codes in several modules at the same time.
• The fault can be intermittent, for example in the rain or over bumps.

Likely causes of the U0104 code

1. Module power or ground: a blown fuse, a corroded ground or a loose power connector.
2. Weak battery or low voltage: it makes modules reboot and lose communication.
3. Module connector with water or corrosion: very common for modules located in wet areas.
4. Damaged network wiring: CAN high or CAN low cut or shorted.
5. Failed cruise control module: only after ruling out everything above.
6. Poorly installed accessory: alarms or trackers wired into the network.

How to diagnose the U0104 code step by step

1. Measure the battery voltage at rest (12.4 to 12.7 V) and with the engine running (13.5 to 14.7 V).
2. Check on the scan tool which modules respond. If the cruise control module does not show up, the fault is in the module or in its connection.
3. Check the module fuses and grounds using the wiring diagram.
4. Measure the network at the OBD2 connector. You should see about 60 ohms between pins 6 and 14 with the battery disconnected, and roughly 2.5 V on each wire with the key on.
5. Inspect the module connector for moisture, corrosion and bent pins.
6. Measure CAN high and CAN low at the module connector. They should have continuity with the OBD2 connector.

How to fix the U0104 code

• Repair the module power, ground or connector.
• Repair the network wiring.
• Replace and program the module if it has failed, which almost always requires programming.
• Clear the codes in all modules and verify.

Technical reference data

• CAN network resistance between OBD2 pins 6 and 14: about 60 ohms.
• 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 U0104 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 U0104