P0403 Code: Exhaust Gas Recirculation (EGR) Control Circuit
The ECU found an electrical fault in the circuit that drives the EGR solenoid or electric EGR valve.
At a glance
Severity: Low
- Meaning
- Exhaust Gas Recirculation (EGR) Control Circuit
- System
- Emission Controls · Powertrain
- Safe to drive?
- Yes, short term
- Typical repair cost
- $40–$1,200
- DIY difficulty
- Easy
P0403 is an electrical code, not a flow code. The ECU switches the EGR control device, either a vacuum solenoid that feeds vacuum to the valve or the motor/coil inside an electronic EGR valve, and it watches the voltage on its own output driver. If that voltage doesn't behave the way an intact circuit should (for example no voltage when the driver is off, which means an open, or a circuit that pulls too much current, which means a short), it sets P0403. That makes wiring, connectors and the solenoid coil the prime suspects, while carbon and clogged passages usually play no role here.
Can I keep driving? Usually safe to drive. Most EGR valves close when they lose power, so the car drives normally; you may notice light pinging under load. If the idle turns rough, the valve may be stuck open and should be checked sooner.
How to read P0403
- P Powertrain
- 0 Generic (SAE)
- 4 Auxiliary emission controls
- 03 Specific fault
Symptoms
- Check engine light on, often with no drivability change
- Light spark knock under load because EGR is no longer working
- Code may come and go over bumps or after rain if a connector is loose or corroded
- Rough idle only in the rarer case where the valve is stuck partly open
- EGR monitor not completing
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Corroded, loose or heat-cracked connector at the EGR solenoid or electric EGR valve
- Open or shorted coil in the EGR vacuum solenoid or electric valve
- Wiring chafed or burned where it runs near the exhaust manifold
- Blown fuse or missing ignition feed to the solenoid
- Valve replaced with a unit of the wrong type or resistance
- Failed output driver inside the ECU
Diagnosis step by step
Identify the control device
Find out whether your engine uses a separate EGR vacuum solenoid (often a small valve on the fender or firewall with two vacuum nipples) or an electronic valve bolted to the intake. The code refers to whichever part the ECU drives directly.
Tools: Flashlight
Inspect the connector and harness
Unplug the connector and look for green corrosion, pushed-back pins and melted insulation. Follow the harness along the engine, paying special attention to any spot close to the exhaust manifold or where it can rub on brackets.
Tools: Flashlight, Screwdriver
Check the power feed
With the key on, one terminal of a simple solenoid should show battery voltage, around 12 V. No voltage means a fuse or feed wire problem, not a bad solenoid; check the fuse the wiring diagram lists for the emission solenoids.
Tools: Multimeter
Measure the coil resistance
Measure across the solenoid or valve terminals and compare with the factory spec. Many EGR vacuum solenoids fall roughly between 20 and 70 ohms; a reading near zero or an open circuit (OL) condemns the part.
Tools: Multimeter
Command it and watch the circuit
Connect a test light between battery positive and the ECU control wire, then use a bidirectional scan tool to command EGR on and off. The light should switch or flicker with the command; if it does, the ECU and wiring work and the solenoid is at fault.
Tools: OBD-II scanner, Multimeter
Clear and recheck
Clear the code, then wiggle the harness with the engine idling and take a short drive. If P0403 returns immediately with no wiring fault found and a good solenoid, have the ECU driver checked before replacing the computer.
Tools: OBD-II scanner
Where the parts are
- 1Ignition coil
- 2Spark plug
- 3Fuel injector
- 4Camshaft sensor
- 5Crankshaft sensor
- 6Engine computer (ECM)
- 7Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Clean or repair connector and terminals | Yes | $40–$150 |
| Repair damaged wiring near the exhaust | No | $100–$300 |
| Replace EGR vacuum solenoid | Yes | $70–$220 |
| Replace electronic EGR valve | No | $250–$700 |
| Repair or replace ECU | No | $400–$1,200 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Chevrolet
GM V6 and Vortec V8 engines with the electric linear EGR valve often log P0403 when the valve's own coil or its connector fails. Because the valve and its position sensor share one housing, a bad valve can also set P0404 or GM's P1404 at the same time.
Field data
| Chevrolet | 4 | Volt |
|---|
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Will fail
P0403 turns on the check engine light and fails OBD-based smog checks in states that test. Clearing it right before the test leaves the EGR monitor not ready, so repair the circuit first.
Frequently asked questions
Does P0403 mean my EGR valve is clogged?
Not usually. P0403 is about the electrical control circuit, so check the connector, wiring and solenoid coil before worrying about carbon. A clogged valve typically sets P0401 or P0404 instead.
Can I test the EGR solenoid myself?
Yes, with a basic multimeter. Measure the coil resistance, check for 12 V on the feed side with the key on, and compare with the spec in a repair manual; an open or shorted coil is easy to spot.
Why does P0403 come back only when it rains?
Water getting into a cracked connector or chafed wire creates a temporary short or high resistance. Seal or replace the connector and repair the insulation, otherwise the fault will keep returning in wet weather.
Sources
- SAE J2012 – Diagnostic Trouble Code Definitions
- ISO 15031-6 – Road vehicles, diagnostic trouble code definitions (EOBD)
- Manufacturer public service information (cross-checked)
- NHTSA Complaints API
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy