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

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.

Bank 1 is the side of the engine with cylinder 1. Inline engines only have this bank.

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

Most likely causes

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

What to check, in order

Start with the simplest. You can tick off each step.

1. Read the soot load and differential pressure with a scanner
2. Gently move the wiring with the engine running and watch whether the reading changes.
3. Check the differential pressure sensor's hoses
4. Check the temperatures before and after the filter
5. Fix any fuel injection or EGR codes before regenerating
6. Perform a regeneration while driving or at a repair shop when the diagnosis allows it

Good to know

• Repair difficulty: medium
• It affects emissions.

What each character of P242E means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 4: Emissions
• 2E: Specific fault in that system

Frequently asked questions

Can I keep driving with code P242E?

If the light is on steadily, take a highway drive or go to a repair shop soon. If the car is in limp mode or the light is flashing, do not push the engine.

What causes code P242E?

The most common causes are: loose or fretted terminal in the sensor connector; harness insulation damaged by exhaust heat, intermittent contact; sensor element breaking up internally.

Related codes

• P242AExhaust Gas Temperature Sensor Circuit (Bank 1 Sensor 3)
• P242BExhaust Gas Temperature Sensor Circuit Range/Performance (Bank 1 Sensor 3)
• P242CExhaust Gas Temperature Sensor Circuit Low (Bank 1 Sensor 3)
• P242DExhaust Gas Temperature Sensor Circuit High (Bank 1 Sensor 3)
• P2085Exhaust Gas Temperature Sensor Circuit Intermittent (Bank 1 Sensor 2)
• P246AExhaust Gas Temperature Sensor Circuit Intermittent/Erratic (Bank 2 Sensor 3)

Sources

• gsi.ext.gm.com: 20OBDG04 Diagnostics
• gsi.ext.gm.com: 25OBDG04B
• law.cornell.edu: 13 CCR 1968.2

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.