U0142 Code: Lost Communication With Body Control Module "B"
A secondary body module went silent; it often runs rear lights, liftgate, trailer and rear comfort features.
Unverified: this manufacturer-specific definition comes from a single source or varies by model. Confirm it with a brand-specific scan tool.
At a glance
Severity: Low
- Meaning
- Lost Communication With Body Control Module "B"
- System
- Module Communication · Network
- Safe to drive?
- With caution
- Typical repair cost
- $10–$1,000
- DIY difficulty
- Moderate
U0142 is logged when other modules stop receiving messages from body control module "B", the second body controller on vehicles that split body functions between two or more units. What "B" controls varies widely by make and model; on many vehicles it is a rear body or liftgate module mounted in the cargo area, behind a quarter trim panel or under the rear seat, handling tail lamps, the power liftgate, rear wiper and defroster, fuel door and trailer lighting. Because these modules live in the back of the car, water in the spare tire well, broken wires in the liftgate hinge harness and badly spliced trailer wiring are typical causes. The exact module assignment is manufacturer-specific, so the service information for your vehicle has to confirm what "B" means.
Can I keep driving? The car is normally safe to drive if the brake lights, tail lamps and turn signals still work. Check them with a helper before driving at night or towing, because a failed rear module can leave you without rear lighting.
How to read U0142
- U Network
- 0 Generic (SAE)
- 1 Module Communication
- 42 Specific fault
Symptoms
- Tail lamps, brake lights or rear turn signals out or flickering
- Power liftgate or trunk release not working
- Rear wiper or rear window defroster dead
- Trailer lights not working through the hitch connector
- Fuel door or rear power windows won't open
- Symptoms appear after heavy rain, a car wash or opening the liftgate
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Water in the cargo area or spare tire well from leaking tail lamp gaskets, liftgate seals or body plugs, soaking the module connector
- Broken wires in the rubber boot between body and liftgate or trunk lid from years of opening and closing
- Aftermarket trailer wiring or hitch module spliced into rear lighting or network circuits
- Blown fuse or poor ground for the rear body module
- Internal module failure
- Low battery voltage
Diagnosis step by step
Identify module "B" for your vehicle
Use the service information or the scan tool's module list to confirm which physical unit is body control module "B" and where it is mounted. Everything else depends on that.
Tools: OBD-II scanner
Check the cargo area for water
Lift the cargo floor and spare tire cover, and remove the trim near the module. Standing water, rust stains or a damp smell mean the leak must be found and sealed, typically at tail lamp gaskets, liftgate seals or rubber body plugs.
Tools: Flashlight, Screwdriver
Flex-test the liftgate harness
Open the liftgate or trunk and peel back the rubber boot at the hinge. Look for cracked insulation and broken strands, and watch live data or a meter on the CAN or power wires while moving the lid; a reading that drops out while flexing confirms a break.
Tools: Multimeter, Flashlight
Disconnect aftermarket trailer electrics
Unplug any add-on trailer module or tow harness and check for splices into the network or rear lamp circuits. Retest with it disconnected; a wrongly connected tow harness can pull down the whole rear network.
Tools: Screwdriver, Pliers
Measure fuses, ground and CAN at the module
Test the module's fuses, voltage-drop test its ground, and measure about 2.5 V on each CAN line at the connector with the key on. If all are good and it still doesn't answer, the module is at fault.
Tools: Multimeter
Repair wiring or replace the module
Broken harness wires are repaired with soldered, heat-shrunk splices staggered so they don't flex in one spot. A replacement module usually needs programming to the VIN and liftgate or trailer configuration.
Tools: Pliers, OBD-II scanner
Where the parts are
- 1Battery
- 2Alternator
- 3Engine computer (ECM)
- 4CAN bus
- 5Transmission
- 6Wheel speed sensor
- 7High-voltage battery
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Replace fuse / clean ground | Yes | $10–$100 |
| Seal cargo area leak and dry connectors | No | $100–$400 |
| Repair liftgate/trunk hinge harness | No | $150–$450 |
| Replace and program body control module B | No | $350–$1,000 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Field data
| Toyota | 2 | Prius Plug-In, Prius V |
|---|
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Depends
U0142 doesn't usually light the check engine light, so smog tests are typically unaffected. A safety inspection will fail the vehicle if brake lights, tail lamps or rear turn signals are out.
Frequently asked questions
Which module is body control module "B"?
It depends on the manufacturer. On many vehicles it is a rear or liftgate body module, on others a second front or in-cabin body unit. The service information or a factory-level scan tool shows the correct one.
Could my new trailer hitch wiring cause U0142?
Yes. Tow harnesses that are spliced into lamp or network wires, instead of using the vehicle's dedicated trailer connector, can overload circuits or disturb the network and knock the rear module offline.
Why does the fault only appear when I open the liftgate?
The harness that feeds the liftgate bends at the hinge every time it opens. Over time the copper strands break inside the insulation, so contact comes and goes with the position of the lid.
Is it dangerous to drive with U0142?
Usually not in itself, but check the rear lighting. If brake lights or turn signals are out, drivers behind you get no warning, which is a real safety risk.
Sources
- SAE J2012 – Diagnostic Trouble Code Definitions
- ISO 15031-6 – Road vehicles, diagnostic trouble code definitions (EOBD)
- Manufacturer public service information (cross-checked)
- NHTSA Complaints API
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy