Powertrain, generic (extended)

P242E Exhaust Gas Temperature Sensor Circuit Intermittent/Erratic (Bank 1 Sensor 3)

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P242E is set when exhaust temperature sensor 3 on bank 1 jumps between two samples faster than real exhaust gas can change, even though each single value is inside the valid range. GM documents this as a quick-change monitor that runs every 100 ms. The 2020 diesel tables look at the resistance step between consecutive samples and fail after 15 of 30 samples; the 3.0 L LZO evaluates the raw temperature step only while the reading is between 140 and 1,070 °C and needs 12 bad samples out of 25. Both are Type B, so the MIL waits for a second faulty trip. Loose terminals, corroded pins and a harness weakened by heat are the usual triggers, though the sensor can also fail internally. CARB asks for such checks on all emission-related inputs. A steady but wrong reading falls under P242B.

Likely causes

Loose or fretted terminal in the sensor connector
Harness insulation damaged by exhaust heat, intermittent contact
Sensor element breaking up internally

Symptoms

  • MIL after the second faulty trip
  • Sensor 3 value jumps in the scan tool live data
  • Code comes and goes, often after rough roads or washing

Repair estimate

DifficultyMediumDIY possible
Parts and labour€0–350
Time0.3–2 h

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

Parts involved

egt sensor b1s3

Related codes

P242AP242BP242CP242DP2085P246A

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