U0140 is "Lost Communication With Body Control Module" — and GM's most recent bulletin on it traces the whole thing to a ground nut that left the factory under-torqued. That one loose ground set eleven codes across the ABS, body, engine and steering modules. GM's correction: tighten it. "No parts are required for this repair." Half an hour of labor.
Jump to a section: What U0140 means · The loose ground case · The two-part code form · Symptoms · Causes and how to confirm each · How it's diagnosed · Parts and labor · Service bulletins · What other pages get wrong · FAQ
What U0140 Means
GM's wording is "Lost Communication With Body Control Module (BCM)." You will also see it written with the reporting module prefixed — GM's own bulletin on the Trailblazer writes it as "ABS U0140," meaning the anti-lock brake module is the one that stopped hearing the body control module.
That prefix matters. The body control module sits at the centre of a great deal of vehicle behaviour, so when it drops off the network, modules all over the car log their own complaints. The result is a dashboard that looks catastrophic and a diagnosis that is often trivial.
The Loose Ground Case — Start Here
GM bulletin 21-NA-215 covers 2021–2022 Chevrolet Trailblazer with the LIH and L3T engines, and it is the cleanest documented example of this code you will find anywhere.
GM's cause statement: "This condition may be caused by a loose ground located at G106. The G106 ground nut may not have been tighten to specifications from the factory."
The correction is to locate the G106 ground, inspect the stud and replace it if needed, then tighten the nut. GM states plainly: "No parts are required for this repair." The labor operation is 5486248 at 0.5 hours. The bulletin includes separate location graphics for each engine.
What that one loose nut produced: U0140, U0100, U0151, U026A, U0415, C2A07, C0501, P0606, P0102, P0300, P0351 and P0352, spread across the ABS, body control, engine control and electric power steering modules. Anyone who started replacing the modules named in those codes would have spent thousands and fixed nothing.
The bulletin's subject line also names the drivability complaints: "Lack of Power When on the Highway, Stall," and a pop noise on heavy acceleration from the engine area.
The Two-Part Code Form: U0140-XX
GM's two-part scheme is confirmed — GM prints codes such as U0422 00 in its bulletins and defines failure byte 71 as "Invalid Data" across all GM models from 2013 to 2022.
No GM-documented sub-types were found for U0140 specifically. The GM bulletins naming this code write it bare. Any 32-row table showing U0140-00 through -1F with distinct meanings is auto-generated boilerplate applied to every code on the sites that publish it, not manufacturer data.
Symptoms of U0140
GM-sourced only:
- Instrument cluster gauges inoperative or fluctuating, and multiple warning lights on the driver information centre
- "Service StabiliTrak", "Traction Control off" and "Service Brake System" messages with a red brake warning lamp — and GM notes this "may happen more at engine start up"
- Lack of power on the highway, and stalling
- A pop noise on heavy acceleration from the engine area
- Complaints of the instrument cluster going out entirely
Widely published U0140 symptoms we could not source to GM for this code, and so do not repeat: power windows and locks inoperative, interior lights staying on, wipers inoperative, HVAC controls dead, and no-crank attributed specifically to U0140. GM lists no-crank and door-lock cycling as symptoms of the bus fault group generally, not as U0140 consequences.
Causes of U0140 — and How to Confirm Each One
| Cause | How to confirm it | Applies to | GM document |
|---|---|---|---|
| Loose ground at G106 — nut not tightened to specification at the factory | Locate G106 using the bulletin's engine-specific graphic, inspect the stud, replace if needed, tighten the nut to spec. No parts required | Trailblazer 2021–2022 (LIH, L3T) | 21-NA-215 |
| Serial data gateway module connector fault | GM's sequence: capture vehicle-wide codes, remove the gateway module's power feed fuse, wait one minute, reinstall it, verify, then inspect the connector for looseness, bent or backed-out terminals or damage. Replace the affected terminal or the connector housing per SI | Silverado / Sierra 1500 2020–2021 | GM Engineering Information bulletin |
| Aftermarket inline speedometer recalibration device spliced into the cluster connector | GM: "This concern could be caused by an aftermarket device installed inline to the IPC connector. This device is used to recalibrate the speedometer for different size wheels/tires. Remove the aftermarket device and retest." Not covered under warranty | Full-size trucks and SUVs 2007–2013 | PIT5120A |
| Bus wiring chafe, open or short; connector corrosion; backed-out terminals; data link resistor | The full nine-cause list GM publishes for this bus fault family applies to U0140 identically. On 2010–2016 Equinox and Terrain, inspect connector X411 behind and to the left of the fuel tank for corrosion | Broad | 08-07-30-021H, PIT5400, PIT5427A |
| Engine wire harness chafing | Inspect at the mapped contact points | 2019–2023 trucks and SUVs | 21-NA-149 |
GM's blanket instruction still governs all of it: "DO NOT replace any control module, wiring harness or component until you have first isolated the cause of the condition."
How U0140 Is Diagnosed
You need vehicle-wide code reading. This code's whole character is that it appears alongside a spread of others, and the spread is the evidence. A generic reader that only talks to the engine module will show you almost none of it. GDS2 or Techline Connect on GM platforms, or a professional aftermarket tool with full GM enhanced coverage.
- Run the Diagnostic System Check — Vehicle and capture every code in every module before touching anything.
- Look at the pattern. Codes scattered across ABS, body, engine and steering point at a shared ground or a harness, not at four failing modules.
- On a 2021–2022 Trailblazer, inspect the G106 ground first. It is a half-hour job with no parts.
- Check the instrument cluster connector for an inline aftermarket speedometer device on older full-size trucks.
- On 2020–2021 Silverado and Sierra, cycle the serial data gateway module's power feed fuse and inspect its connector.
- On 2010–2016 Equinox and Terrain, inspect connector X411 for corrosion.
- Resolve the non-communication codes before the U-codes, then re-evaluate.
One caution GM itself attaches to the Engineering Information bulletin on this: "THIS IS NOT A RECALL." It is diagnostic guidance, not a free repair programme.
Parts and Labor
| Repair | Parts | Price | GM labor operation | Time |
|---|---|---|---|---|
| G106 ground repair (Trailblazer) | None required — GM states this explicitly | — | 5486248 | 0.5 hr |
| Serial data gateway module connector inspection | Terminal or connector housing per SI if damaged | — | 5486118 | 0.5 hr |
| Connector inspection | — | — | 2680278 | 0.1–0.3 hr |
| Body control module | 13531840 — fits Silverado 1500 2021, Silverado 1500 LTD 2022, Silverado 2500/3500 HD 2021–2023 | $165.64 MSRP | — | — |
| Engine harness chafing inspect and repair | Tape, sleeves, clips per 21-NA-149 | — | 5480728 | 1.2 hr |
| Wrap and secure engine wire harness | As above | — | 5486188 | 1.3 hr |
The body control module is listed because it is a real GM part with verified fitment, not because it is the answer to this code. Body control modules are VIN-specific and require programming and setup after fitting. GM's documented repairs for U0140 are a ground nut, a connector, and a wire — none of which involve one.
GM Bulletins That Name U0140
| Bulletin | Subject | Vehicles |
|---|---|---|
| 21-NA-215 | Lack of power on the highway, stall, pop noise — loose G106 ground. No parts required | Trailblazer 2021–2022 (LIH, L3T) |
| 08-07-30-021H | The bus fault family bulletin — nine causes and the do-not-replace instruction | Trucks and Corvette 2007–2014 |
| PIT5120A | Aftermarket inline speedometer recalibration device at the cluster connector — not warranty covered | Full-size trucks and SUVs 2007–2013 |
| 21-NA-149 | Engine wire harness chafing | 2019–2023 trucks and SUVs |
No special coverage and no NHTSA recall names U0140 on the models we checked.
What Other U0140 Pages Get Wrong
- Leading with "replace the body control module." GM's documented repairs for this code are a ground nut, a gateway connector, an aftermarket device removal and a wire repair. Not one of them is a module.
- Symptom lists GM does not support — power windows dead, interior lights stuck on, wipers inoperative, HVAC dead. These get attributed to U0140 specifically; GM does not.
- Omitting the aftermarket device cause. If someone fitted an inline speedometer corrector for larger tyres, GM documents that as a cause and states the resulting issues are not covered under warranty. That is worth knowing before a warranty claim is filed.
- The 32-row sub-type table. Auto-generated boilerplate with no manufacturer attribution.
Frequently Asked Questions
Do I need a new body control module for U0140?
Probably not. Every repair GM documents for this code is something else — a loose ground nut, a serial data gateway connector, an aftermarket device that needs removing, or a chafed wire. GM's standing instruction is not to replace any module until the cause has been isolated.
My 2021 Trailblazer has U0140 and a dashboard full of warnings. What is it?
Check the G106 ground first. GM bulletin 21-NA-215 covers exactly that vehicle and documents a ground nut that was not tightened to specification at the factory, producing eleven codes across four modules. The correction is to tighten it — no parts, half an hour.
Why did U0140 come with so many other codes?
Because the body control module is central to how the vehicle behaves, so when it drops off the network, modules across the car log their own complaints. That is why a scattered code pattern points at a shared ground or harness rather than several separate failures. In GM's documented case, one loose nut set codes in the ABS, body, engine and steering modules simultaneously.
Can an aftermarket speedometer corrector cause U0140?
Yes, and GM documents it. On 2007–2013 full-size trucks and SUVs, a device installed inline to the instrument cluster connector to recalibrate the speedometer for different wheel or tyre sizes is a named cause. GM's instruction is to remove it and retest, and GM states that issues caused by that device are not covered under warranty.
What does the -00 mean in U0140-00?
No GM-documented sub-types exist for U0140. GM's bulletins write the code bare, so a -00 is the generic "no sub type information" value rather than a specific fault mode.
Can I drive with U0140?
Not comfortably, and not far. GM's own bulletin subject line for this code names lack of power on the highway and stalling. Combined with the brake and stability warnings GM documents, this is a code to have looked at rather than live with.
How much should a U0140 repair cost?
In the best-documented case, remarkably little: GM labor operation 5486248 at 0.5 hours with no parts at all. The gateway connector inspection is another 0.5 hours. A harness repair runs 1.2 to 1.3 hours. Those are the figures to weigh a module quote against.
Why does it happen more at startup?
GM notes that on the platforms covered by PIT5120A, the StabiliTrak, traction control and brake system messages "may happen more at engine start up." Startup is when bus traffic and current draw are highest, so a marginal ground or connection is most likely to fail its test then.
Shop the Parts Mentioned
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KONNWEI KW850 OBD2 Scanner — $83.11, retrieves generic (P0, P2, P3, U0) and manufacturer-specific (P1, P3, U1) codes, so it reads network codes like this one. Live data with graphing, freeze frame, O2 and EVAP tests, battery voltage check, and a built-in DTC lookup library. Engine-system coverage only — it does not read ABS or airbag modules.
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VDIAGTOOL BT500 Battery Tester — $57.53, tests battery health, cranking and charging on 6V/12V/24V systems with ripple analysis and a voltage waveform — rules out low system voltage, a common trigger for spurious module-communication codes.
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Battery Terminal Cleaning Brush — clears corrosion contributing to voltage-related faults.
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ACDelco Gold Negative Battery Cable — for replacing corroded terminals or grounds.
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95-Piece Mechanics Tool Set (Metric & SAE) — for BCM wiring and connector access.