P040E: EGR Temperature Sensor A Circuit Intermittent/Erratic

EGR temperature sensor A measures the gas temperature in the EGR path – for cooler monitoring, component protection and the EGR model. Whether it sits before or after the cooler depends on the maker: GM diesels have sensor A after and B before the cooler, Ford diesels sensor B after it. Like a coolant sensor it is an NTC, so a low voltage means hot. P040E means the signal jumps. GM diesels of 2016–18 set it when the measured resistance changes by more than 25 Ω between two samples 100 ms apart – faster than any real temperature change, so a loose contact or a cracked sensor is the cause (40 of 50 samples, MIL after two trips). Ford and GM's earlier Duramax LML do not use the code.

Medium severity. Can I keep driving?You can normally drive in moderation, but get it repaired soon: if the valve is stuck open, the engine may idle very poorly.

Symptoms

Check engine light on, may come and go
No change in driving

Most likely causes

Loose contact in the connector or chafed wire
Sensor with an internal hairline crack
Corroded pins

What to check, in order

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

Check the connector and any vacuum hoses
Gently move the wiring with the engine running and watch whether the reading changes.
Use live data to compare the commanded opening with the actual opening
Clean the valve and passages if they are clogged with carbon
Test the actuator with the scanner
Replace the valve if it still does not follow the command after cleaning

Good to know

Repair difficulty: easy
It affects emissions.

What each character of P040E means

P: Powertrain: engine and transmission
0: Generic code: same on every make
4: Emissions
0E: Specific fault in that system

Frequently asked questions

Can I keep driving with code P040E?

You can normally drive in moderation, but get it repaired soon: if the valve is stuck open, the engine may idle very poorly.

What causes code P040E?

The most common causes are: loose contact in the connector or chafed wire; sensor with an internal hairline crack; corroded pins.

Related codes

Sources

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.