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U040A Invalid Data Received From Air Conditioning Control Module

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

J2012 separates the air conditioning control module, which governs the refrigerant side with compressor, pressures and, in electrified cars, an electric compressor drive, from the HVAC module that handles blower, flaps and set temperature (invalid data from that one is U0424). U040A is stored when frames from the A/C unit arrive but carry values the receiver cannot trust, such as a failed counter or checksum or a signal outside its range. No manufacturer documents U040A publicly. GM confirms the module itself: the 2011 Saab 9-5 code list carries U010F for lost contact with it, and GM's generic routine for U0400-U05FF reprograms the named module and replaces it only if the code returns. The compressor is likely held off, so cooling and demisting suffer; engine and emissions stay unaffected. U010F is lost contact.

Likely causes

Software of the A/C control module or of the receiver out of step
Faulty pressure or temperature input making the module send invalid values
Disturbed bus line, poor ground or low supply voltage at the module
A/C control module internally faulty

Symptoms

  • Air conditioning blows warm, compressor stays off
  • Windows demist slowly

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–900
Time0.3–2 h

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

Parts involved

ac control module

Related codes

U010FU0164U0424

References: saabwisonline.com, saabwisonline.com, en.wikipedia.org.