P0403🌫 Emissions / EGRDrive with caution, fix soon

P0403: EGR Control Circuit (Meaning, Causes, Fixes)

Reviewed 2026-10-23 · Based on 2 cited source(s)

What P0403 means

The EGR system feeds a small amount of exhaust back into the cylinders to lower combustion temperature and cut oxides of nitrogen (NOx). RepairPal says it is usually no more than 10 percent of the intake air and keeps combustion below about 2500 F, where NOx forms. On many engines the EGR valve is opened by vacuum, and an electric vacuum solenoid decides when vacuum reaches the valve. OBD-Codes.com says the solenoid gets ignition voltage and the powertrain control module (PCM) turns it on by grounding its control circuit through a driver. When the solenoid is on, the control circuit should read close to zero volts; when it's off, it should read near battery voltage. Each driver has a fault circuit the PCM watches, and if it doesn't see the right voltage at the right time, it sets P0403. RepairPal says the same thing: the PCM isn't seeing the proper EGR vacuum solenoid voltage when it allows or denies vacuum to the valve. It is a generic OBD-II code, though repair steps vary by make and model. The sources differ in a few ways. Both use the technical name Exhaust Gas Recirculation "A" Control Circuit, but both page headings also call it EGR Circuit Malfunction. RepairPal's short summary describes it as the PCM not detecting the EGR flow it requested, which reads more like a flow problem, and it lists flow-side causes (carbon in the passages, the EGR valve, feedback sensors) that OBD-Codes.com doesn't. OBD-Codes.com treats it as an electrical fault in the solenoid circuit. For symptoms, OBD-Codes.com mentions misfire, rough idle or stalling if the solenoid is stuck open, while RepairPal mentions pinging under load. RepairPal rates it Moderate; OBD-Codes.com gives no rating.

Severity: can I keep driving?

Drive with caution, fix soon

Get it diagnosed within a reasonable time. RepairPal rates P0403 Moderate, meaning it may not threaten safety or drivability right away. OBD-Codes.com gives no severity rating and says a control circuit fault usually causes nothing beyond the check engine light. If the engine misfires on acceleration, idles rough, stalls, or pings badly under load, get it checked sooner.

Common symptoms

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

  1. Faulty EGR vacuum solenoid (both sources)
  2. Open, chafed or damaged wiring causing excess resistance in the PCM-controlled ground circuit (OBD-Codes.com)
  3. Poor connection, worn or loose pins, or water intrusion at the EGR solenoid connector (OBD-Codes.com)
  4. Debris inside the solenoid holding it open or closed (OBD-Codes.com)
  5. Loss of supply voltage to the EGR solenoid (OBD-Codes.com)
  6. Lack of proper vacuum or electrical signal to the EGR valve (RepairPal)
  7. Carbon-restricted EGR passages or a defective EGR valve (RepairPal only)
  8. Bad feedback from the MAP sensor, DPFE sensor, EGR valve position sensor or EGR temperature sensor (RepairPal only)
  9. Faulty PCM (OBD-Codes.com, listed last)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

  1. Record the freeze frame data so you know the conditions when the code set, and try to repeat them with a data-streaming scan tool connected (RepairPal).
  2. With the ignition on and the engine off, use a scan tool to command the EGR solenoid on. Listen or feel for a click (OBD-Codes.com).
  3. If it clicks, OBD-Codes.com says to check current draw on the ground circuit; it should be under one amp. If it is, the fault is likely intermittent. If not, check whether you can blow lightly through the activated solenoid (a blockage means replace it), then with the solenoid and PCM connector unplugged, check that resistance from the control wire to battery ground is infinite. Anything else means a short to ground to repair.
  4. If it doesn't click, OBD-Codes.com says to unplug the solenoid, connect a test light across the two connector wires and command the solenoid on. If the light comes on, replace the solenoid. If not, check for 12 volts on the supply wire, then manually ground the control wire: if the light then works, repair an open in the control circuit; if not, replace the solenoid.
  5. If the circuit tests good, RepairPal's flow checks apply: at 3000 RPM, opening the EGR valve fully should drop manifold vacuum by at least 3 inches of mercury, and the engine should stumble or die when the valve is opened at idle. It also suggests checking the EGR position sensor, DPFE sensor and front oxygen sensor response.
  6. Don't assume it's the valve. RepairPal says P0403 is often not a problem with the EGR valve itself.

Typical fixes

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

  • The engine misfires, idles rough, stalls or pings
  • You don't have a scan tool that can command the EGR solenoid
  • You're not comfortable doing voltage, current or resistance checks with a meter
  • The code returns after replacing the solenoid
  • You need to pass an emissions inspection soon

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Can I drive with P0403?

Usually yes for a short time, if the engine runs normally. RepairPal rates it Moderate and both sources say there are often no symptoms beyond the check engine light. Get it checked sooner if the engine misfires, idles rough, stalls or pings.

Is P0403 a bad EGR valve?

Usually not. P0403 is about the circuit that controls the EGR vacuum solenoid. OBD-Codes.com points to the solenoid and its wiring, and RepairPal says P0403 is often not the EGR valve itself. Test the solenoid circuit before buying a valve.

What's the difference between P0403 and P0404?

P0403 means the PCM saw the wrong voltage in the EGR solenoid control circuit. P0404 is EGR "A" Circuit Range/Performance, which usually means the valve's commanded and actual position or flow don't agree.

How much does it cost to fix P0403?

Neither source gives a repair cost for P0403. It can be a wiring repair, a connector, a solenoid or, less often, other EGR parts, so diagnose it first.

Sources

  1. OBD-Codes.com: P0403 Exhaust Gas Recirculation Circuit Malfunction
  2. RepairPal: P0403 Exhaust Gas Recirculation "A" Control Circuit (rated Moderate)

Last reviewed 2026-10-23. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.