OBD-II trouble code
U0442: Invalid Data Received From ECM/PCM 'B'
A module is receiving messages from the secondary engine/powertrain computer (ECM/PCM 'B'), but the data inside them is implausible or out of range. The link is alive; the content is wrong. The 'B' counterpart to U0401.
Quick facts
- System
- Network
- Category
- Network Communication
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $1,200
- DIY difficulty
- Shop recommended
What does U0442 mean?
Most vehicles have one engine control module, but some — larger engines, certain diesels, and vehicles that split powertrain duties across two controllers — use a second unit designated ECM/PCM 'B'. It works alongside the primary ECM/PCM 'A' and shares data with it and the rest of the network. U0442 sets when a receiving module is still hearing from ECM/PCM 'B', but the data in its messages is invalid: a value is out of range, implausible, or contradicts what other modules see. The link is alive; the content can't be trusted. That is the key difference from a lost-communication code, which means the module has gone completely silent. Its 'A' counterpart is U0401 (invalid data from ECM/PCM 'A').
Because the fault is bad data rather than a dead bus, the causes cluster around whatever makes the secondary powertrain module broadcast wrong information. Low system voltage or a poor ground is a very common trigger — powertrain modules are sensitive to supply voltage. Corroded connectors, water intrusion, or chafed bus wiring can corrupt otherwise-good messages in transit. A failing sensor feeding the 'B' module, or software that is outdated, corrupted, or was never properly re-flashed after a module or engine-management replacement, can push implausible values onto the network. Electrical noise on the bus is another possibility.
Symptoms range from just a check engine light to real driveability trouble, depending on what ECM/PCM 'B' controls on the specific vehicle. You may see reduced power or a limp-mode fail-safe, rough running, or warning messages, along with companion powertrain codes. The vehicle often remains driveable, but because the secondary module can be responsible for real engine functions, treat U0442 as more than a nuisance. Read the full list first — a companion powertrain or sensor code frequently names the real root cause, and low voltage is worth ruling out early because it is a common, inexpensive fix.
Common causes
- Low system voltage, a weak battery, or a poor ground — a very common powertrain-module trigger
- Corroded connectors, water intrusion, or chafed bus wiring corrupting messages
- A failing sensor feeding the secondary ECM/PCM an implausible value
- Outdated, corrupted, or mismatched software after a module or engine-management replacement
- ECM/PCM 'B' replaced without proper programming
- Electrical noise on the bus corrupting messages
- Damaged bus wiring between the powertrain controllers
- Internal fault within ECM/PCM 'B'
Symptoms
- Check engine light, sometimes with a reduced-power warning
- Reduced power or limp-mode fail-safe in some cases
- Rough running or hesitation depending on what ECM/PCM 'B' controls
- Warning messages on the dash
- Companion powertrain or sensor codes stored alongside U0442
Diagnostic steps
- 1.Read ALL stored codes first — U0442 is often secondary to a powertrain or sensor code that names the real fault.
- 2.Load-test the battery and check charging voltage and grounds; low voltage is a leading powertrain-module cause.
- 3.Inspect the ECM/PCM 'B' connectors and area for corrosion, water intrusion, and loose pins.
- 4.Check the bus wiring between the powertrain controllers for chafing and damage.
- 5.Use live data to look for a specific powertrain parameter reporting an out-of-range or implausible value.
- 6.Verify ECM/PCM 'B' has the correct, current calibration, especially after any recent replacement.
- 7.Address companion powertrain codes before condemning the module.
Repair cost
$100 – $1,200
Cost depends on what is producing the bad data. Correcting low voltage, a weak battery, or a bad ground is often $150-$400. Repairing corroded connectors or bus wiring varies with access. A failing sensor is typically $150-$400 installed. A module reflash is $100-$300, and ECM/PCM replacement with programming is the expensive case at $500-$1,200 — but that should only follow thorough diagnosis, since U0442 is frequently secondary and low voltage is a common, cheap fix.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with module communication / can bus diagnosis preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.