Damaged, chafed, or corroded wiring in the ion sense circuit between the module and the ECM; Faulty ion sense module or its internal electronics; Poor electrical ground connection for the ion sense module; CAN (Controller Area Network) bus communication fault affecting the module's messages; Low or unstable battery voltage causing the module to send corrupted data; Water intrusion or connector contamination at the ion sense module; Failed spark plug or ignition coil that distorts the ionization signal

DTC codes / U09xx · Network communication / U0901

U0901Invalid Data from Ion Sense Module

Q: What does code U0901 mean?

Invalid Data from Ion Sense Module. U0901 means the engine control module (ECM) received invalid or corrupted data from the ion sense module over the vehicle's communication network. The ECM expects a clean, plausible signal that indicates ionization current at the spark plugs, but the message it received failed its internal validity check, so the ECM set this communication fault.

U0901 means the engine control module (ECM) received invalid or corrupted data from the ion sense module over the vehicle's communication network. The ECM expects a clean, plausible signal that indicates ionization current at the spark plugs, but the message it received failed its internal validity check, so the ECM set this communication fault.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaNetwork communication

Symptoms you may notice

Illumination of the malfunction indicator lamp (MIL) with no other obvious driving complaint
Rough idle or intermittent misfire under light load
Hesitation or stumble during acceleration
Reduced fuel economy over time
In rare cases, the engine may enter a limp-home mode with limited power
Often no symptoms besides the warning light

Common causes, most likely first

Damaged, chafed, or corroded wiring in the ion sense circuit between the module and the ECM
Faulty ion sense module or its internal electronics
Poor electrical ground connection for the ion sense module
CAN (Controller Area Network) bus communication fault affecting the module's messages
Low or unstable battery voltage causing the module to send corrupted data
Water intrusion or connector contamination at the ion sense module
Failed spark plug or ignition coil that distorts the ionization signal

How to diagnose and fix it

Scan all modules for stored and pending codes, and record freeze-frame data to understand when U0901 set
Inspect the ion sense module connector and wiring for corrosion, chafing, or loose pins, and repair as needed
Check battery voltage and charging system output to rule out low-voltage communication errors
Verify the ion sense module ground circuit with a multimeter and clean or tighten the ground point
Perform a wiggle test on the ion sense harness while monitoring live data to catch intermittent faults
If wiring and power are good, substitute a known-good ion sense module and clear codes to see if U0901 returns
After repair, clear codes and complete a drive cycle to confirm the fault does not reset

What ion sense data really tells the ECM

The ion sense module measures ionization current at the spark plug to detect misfire and knock, so a failing spark plug can corrupt the signal and set U0901 even when the module itself is healthy.
A weak or aging battery often causes modules to transmit invalid data frames, so always load-test the battery before condemning the ion sense module.
U0901 can be stored alongside misfire codes like P0300, but the misfire may be the cause rather than the effect, so diagnose the ignition system first.
Some vehicles use the ion sense signal for knock detection, so ignoring U0901 can lead to undetected pre-ignition and long-term engine damage.
A poor ground at the module can produce intermittent invalid data that only appears on cold starts or over rough roads, making a wiggle test essential.

Can I keep driving with U0901?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy acceleration or towing until the fault is repaired. If the engine runs rough or enters limp mode, stop driving and arrange a tow to prevent further damage.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.