P04E9: EGR Temperature Sensor D Circuit Intermittent/Erratic

Exhaust gas recirculation (EGR) routes part of the exhaust back into the intake to lower combustion temperature and NOx. Sensor D is the fourth of up to four EGR temperature sensors, conceivable on engines with high- and low-pressure EGR and a sensor before and after each cooler; it is usually an NTC whose low voltage means hot. No manufacturer document available to us uses sensor D; the description follows CARB and Ford's checks on sensor B as a comparison. P04E9 means the signal briefly leaves its valid range or changes impossibly fast – typically a loose contact. Ford detects such sporadic faults on other sensors with short limit violations of about 0.4 s.

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
Usually no change in driving

Most likely causes

Loose contact in connector or harness (vibration, heat)
Sensor with an internal hairline crack
Chafed harness
Module or ground connection

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: medium
It affects emissions.

What each character of P04E9 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
4: Emissions
E9: Specific fault in that system

Frequently asked questions

Can I keep driving with code P04E9?

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 P04E9?

The most common causes are: loose contact in connector or harness (vibration, heat); sensor with an internal hairline crack; chafed harness.

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.