P0407: EGR Sensor B Circuit Low

Exhaust gas recirculation (EGR) routes part of the exhaust back into the intake to lower combustion temperature and NOx. What EGR sensor B is depends on the manufacturer – on systems with a second valve or pressure sensor it is that second sensor. GM's diesels of 2017/18 use P0407 for the coolant temperature sensor at the inlet of the high-pressure EGR cooler: low means a resistance below 55 Ω, i.e. very hot or shorted to ground, MIL after two trips. No manufacturer document available to us uses the code for a second position sensor. 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
EGR or EGR cooler protection possibly restricted

Most likely causes

Sensor wire shorted to ground
Sensor faulty
Connector corroded (near coolant or exhaust)
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
With the connector unplugged, check whether the signal wire is making contact with ground.
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 P0407 means

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

Frequently asked questions

Can I keep driving with code P0407?

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 P0407?

The most common causes are: sensor wire shorted to ground; sensor faulty; connector corroded (near coolant or exhaust).

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.