P0405: EGR Sensor A Circuit Low

Exhaust gas recirculation (EGR) routes part of the exhaust back into the intake to lower combustion temperature and NOx. EGR sensor A is usually the valve position sensor with a 5 V supply; on Ford until about 2011 it was the DPFE differential pressure sensor. P0405 means its signal is below the lower limit – GM 2018 below 11 % of 5 V (MIL after two trips), Ford below 5 % of full scale for 4 s, Saab below 0.26 V. The cause is a short to ground or an open signal or 5 V wire. EGR position control is then switched off.

Symptoms

• Check engine light on
• EGR switched off
• Diesel: possibly reduced power
• Otherwise hardly noticeable

Most likely causes

• Wire or connector to the EGR valve open or shorted to ground
• Position sensor in the EGR valve faulty (usually one unit with the valve)
• Older Ford: DPFE sensor faulty
• Shared 5 V reference shorted

What to check, in order

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

1. Check the connector and any vacuum hoses
2. With the connector unplugged, check whether the signal wire is making contact with ground.
3. Use live data to compare the commanded opening with the actual opening
4. Clean the valve and passages if they are clogged with carbon
5. Test the actuator with the scanner
6. Replace the valve if it still does not follow the command after cleaning

Good to know

• Repair difficulty: easy
• It can trigger limp mode.
• It affects emissions.

What each character of P0405 means

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

Frequently asked questions

Can I keep driving with code P0405?

You can reach a repair shop without rushing, but do not push the engine. Because the control module does not know where the valve is, it may disable it or limit power.

What causes code P0405?

The most common causes are: wire or connector to the EGR valve open or shorted to ground; position sensor in the EGR valve faulty (usually one unit with the valve); older Ford: DPFE sensor faulty.

Related codes

• P0406EGR Sensor A Circuit High
• P0409EGR Sensor A Circuit
• P046DEGR Sensor A Circuit Intermittent/Erratic
• P0403EGR A Control Circuit/Open
• P0404EGR A Control Circuit Range/Performance

Sources

• gsi.ext.gm.com: 18OBDG04 Engine Diagnostics
• fordservicecontent.com: OBD Operations Summary Gasoline 2020 2023
• newtonnet.co.uk: fordobd2012
• saabwisonline.com: dtc p0405 or p0406

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.