Network, generic

U05A8 Invalid Data Received From NOx Sensor C

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

A third NOx sensor appears on exhaust systems with two SCR stages, where sensor C watches the gas after the second catalyst. GM's 2025 ECM tables (25OBDG04B) are the public example: the engine controller checks alive rolling count and checksum of the post-second-catalyst NOx signals, eight failures in 18 samples or three in ten depending on the signal, with battery voltage of at least 11 V for 5 s, and logs U05A8 as Type B. The companion 25OBDG04A set has no such entry. U02A1 covers loss of sensor C messages, U05A9 the case where sensor C refuses engine data, U059E and U059F the first two sensors. The second SCR stage cannot be judged while the code is present.

Likely causes

Control unit of NOx sensor C faulty
Harness or connector of the rearmost sensor damaged
Sensors swapped between positions during repair

Symptoms

  • Check engine light after two trips
  • SCR monitor for the second catalyst incomplete

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€150–900
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

nox sensor c

Related codes

U02A1U05A9U059EU059FU0352

References: gsi.ext.gm.com, law.cornell.edu.