U0901

Code

Generic U — Network/User

Invalid Data from Ion Sense Module

Brand: Generic

Type: U — Network/User

Views: UK: 21 EN: 29 RU: 25

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Page language: EN

Causes

Faulty ion-sense module (internal failure or firmware error)
Corroded, loose, or damaged connector or wiring to the ion-sense module
Open, shorted, or high-resistance power supply or ground to the module
CAN or other vehicle network wiring fault (short to battery/ground, open, high resistance)
Electromagnetic interference or intermittent connection causing corrupted packets
Faulty ECM/PCM or gateway module interpreting data incorrectly

Symptoms

MIL (Check Engine Light) illuminated
Stored U0901 and possibly other network or sensor-related codes
Incorrect or missing ion-sense data displayed by scan tool (garbage values, out-of-range, or no response)
Driveability concerns if system depends on ion-sense input (misfire detection, ignition timing, rough idle)
Intermittent faults that may clear and return, or persist until repaired

What to check

Use a capable scan tool to read U0901 and any accompanying codes or freeze frame data
Attempt to communicate with the Ion Sense Module using manufacturer-specific functions; note if the module responds
Inspect the ion-sense module connector and wiring for corrosion, bent pins, heat damage, or water intrusion
Check battery voltage and verify stable supply voltage to the module with ignition on
Verify solid ground(s) at the module (measure continuity to chassis/negative battery)
Measure CAN (or other network) bus voltages and waveform quality with an oscilloscope if available (look for proper recessive and dominant levels and clean edges)

Signal parameters

Module supply voltage (key ON) — nominal battery voltage (~12V with engine off)
Module ground continuity to chassis/negative battery — low resistance
CAN High and CAN Low idle voltages — within manufacturer specification (look for expected recessive levels)
CAN bus differential waveform — clean dominant and recessive edges, correct bit timing if oscilloscope available
Presence and frequency of expected CAN messages/IDs from ion-sense module (seen with a scan tool or bus monitor)
Ion-sense signal amplitude/timing (if accessible) — within expected ranges for that sensor

Diagnostic algorithm

Verify the code: Read freeze frame and stored codes; record module IDs and any related U or P codes.
Check for network-wide issues: See if other modules report communication faults. If multiple nodes are affected, focus on CAN bus and battery/ground.
Attempt to communicate: Use a scan tool to request data from the ion-sense module. Note whether it responds and if data values look plausible or corrupted.
Visual inspection: Turn ignition off, disconnect battery if required by vehicle procedure, inspect connectors and wiring to the ion-sense module for damage, corrosion, water entry, or loose terminals.
Power/ground tests: With ignition ON, measure supply voltage at the module connector and check key ground(s). Repair any open or high-resistance circuits.
Communication line tests: With ignition ON, measure CAN High/Low voltages at the module. If readings are out of range or missing, trace wiring for short/open. Wiggle wiring while monitoring to find intermittent faults.
Signal integrity: If available, use an oscilloscope or CAN bus analyzer to view message traffic and waveform quality. Look for missing packets, CRC errors, or noise.
Isolate the module: If wiring and bus are good, disconnect the ion-sense module and check if related codes change or if bus behavior alters (follow manufacturer-safe isolation steps).
Substitute or reflash: If possible, reflash/update module software per manufacturer guidance or substitute a known-good ion-sense module to confirm fault.
Clear codes and road test: After repairs, clear codes and confirm the fault does not return under varied operating conditions.
Safety note: Follow vehicle manufacturer procedures for handling battery, airbags, and SRS when disconnecting modules or performing repairs.

Likely causes

Connector contamination or bent pins at the ion-sense module
Intermittent CAN-H or CAN-L connection (loose splice, chafe, water ingress)
Low or missing module supply voltage or poor ground
Ion-sense module internal fault (most common if wiring and bus voltages are normal)
Recent repairs or aftermarket device installed on the vehicle network