P0405

Exhaust Gas Recirculation (EGR) Sensor "A" Circuit Low

Car Fault Codes Emissions & exhaust

Can you still drive? Yes, normally

Who can fix it? Needs a workshop

Typical repair time 30 minutes – 3 hours

Typical cost SAR 100 to 1,800

What it means

The engine computer has detected that the EGR sensor signal, usually the valve position sensor or a pressure sensor, is below its allowed minimum. This usually means a short to ground, a missing reference voltage or a failed sensor, so the computer cannot monitor the system properly.

Symptoms4

Check engine light on.
Often no clear driving symptoms.
The computer may disable EGR, causing light knocking under load.
Failed emissions test.

Possible causes5

Signal wire shorted to ground from chafing or exhaust heat.
Open reference voltage supply to the sensor.
Failed sensor, which is built into the EGR valve on many vehicles.
Corroded or loose connector.
Another sensor sharing the same reference circuit shorting and pulling the voltage down.

How to diagnose5

Watch the sensor signal on a scan tool with the ignition on and compare it with the manufacturer specification.
Measure the reference voltage and ground at the sensor connector.
Unplug the sensor and watch the reading; if it stays low, the fault is in the wiring.
Gently move the wiring while watching the reading to find an intermittent short.
If other sensor codes are present, check the shared reference circuit.

How to fix5

Clean or repair the connector.
Repair the shorted or open wire and route it away from heat.
Replace the failed sensor, or the other sensor pulling the reference down.
Replace the EGR valve if the sensor is built into it.
Clear the codes and confirm the reading is back in range.

Repair cost

0–500

500–2,000

2,000–5,000

5,000+

In Saudi riyals; the highlighted part is the expected range for this fault.

The cost is low for a wire or connector fault, and rises when the sensor is built into the EGR valve and the whole valve must be replaced.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions

Does this code mean the EGR valve is dirty?

No, this is an electrical code for the sensor signal. Carbon fouling usually causes flow codes such as P0401.

Why are other sensor codes stored with it?

Some sensors share one reference supply, and a short in one pulls the voltage down for all of them, so look for the shared cause first.

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This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.

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