P040D: EGR Temperature Sensor A Circuit High

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. P040D means the signal is above its upper limit – very cold or, far more often, an open circuit (connector off, broken wire). Thresholds: GM's Duramax LML above 4.84 V for 5 s, GM 2014 above 4.98 V, GM 2018 a resistance above 1268 Ω (40 of 50 samples, MIL after two trips); Ford diesel lists the code without figures. A substitute value is used.

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
Usually no change in driving
Substitute value used, EGR cooler check suspended

Most likely causes

Connector off, broken wire or open circuit
Sensor open internally
Ground wire open or short to positive
Engine module input

What to check, in order

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

Check the connector and any vacuum hoses
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
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 P040D means

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

Frequently asked questions

Can I keep driving with code P040D?

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 P040D?

The most common causes are: connector off, broken wire or open circuit; sensor open internally; ground wire open or short to positive.

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.