P0405 is an OBD-II trouble code that points to a problem in your vehicle’s EGR (Exhaust Gas Recirculation) system, specifically the EGR position sensor circuit. When this code sets, your engine computer is seeing a signal that’s lower than it expects, which usually means a sensor, wiring, or connector issue. You might notice a check engine light, rough idle, or even poor fuel economy, but sometimes the car still feels “normal.” Understanding what P0405 means and how to diagnose it can save you time, money, and frustration.
What Does P0405 Mean?
P0405 stands for “Exhaust Gas Recirculation Sensor A Circuit Low.” In simple terms, your ECU commands the EGR valve to open and expects to see a matching feedback signal from the EGR position sensor. With P0405, the ECU sees a voltage that’s too low (often near 0 volts), so it assumes the circuit or sensor isn’t working correctly.
This usually points to a failed EGR valve with an integrated position sensor, damaged wiring, poor electrical connections, or sometimes an issue inside the ECU. While it’s not typically an emergency drivability code, it does affect emissions and can cause rough running in some vehicles.
Quick Reference
- Code: P0405
- Definition: EGR Sensor A Circuit Low
- Main system: Exhaust Gas Recirculation (EGR)
- Common causes: Bad EGR valve/sensor, wiring faults, poor connections
- Risk level: Low to moderate (emissions and drivability)
- Typical repairs: EGR valve replacement, wiring repair, connector cleaning
Real-World Example / Field Notes
In the shop, I see P0405 a lot on higher-mileage vehicles that spend time in stop-and-go traffic. A typical case: a mid-2000s sedan comes in with a check engine light but no major drivability complaints. Scan tool shows P0405 stored and sometimes a companion EGR code. Live data reveals the EGR position sensor stuck at 0.1 volts no matter what the ECU commands.
After a quick visual inspection, the EGR connector is packed with corrosion from years of moisture and road salt. Cleaning the connector and repairing one broken wire brings the voltage back to normal, and the code doesn’t return. Other times, the EGR valve itself is internally worn, and replacement is the only reliable fix.
Symptoms of P0405
- Check engine light on: The MIL/SES light is usually the first and most obvious sign.
- Rough idle: You may feel shaking or unstable idle speed, especially when the engine is warm.
- Hesitation or stumble: Light acceleration can feel jerky if the EGR system is misbehaving.
- Poor fuel economy: Incorrect EGR operation can reduce efficiency over time.
- Failed emissions test: P0405 will typically cause an automatic emissions inspection failure.
- Engine pinging (spark knock): In some engines, improper EGR flow can lead to light knocking under load.
- No noticeable symptoms: Many drivers feel no difference other than the warning light.
Common Causes of P0405
Most Common Causes
- Faulty EGR valve with built-in position sensor: Many modern EGR valves have an integrated sensor. Internal wear, contamination, or failure can cause a permanently low signal.
- Damaged wiring to the EGR sensor: Chafed, broken, or shorted wires between the EGR and ECU can pull the signal voltage down.
- Corroded or loose EGR connector: Moisture, oil, and dirt can corrode terminals, increasing resistance or creating an intermittent low-voltage condition.
- Poor ground or 5V reference issues: If the sensor’s ground or reference voltage is compromised, the return signal will be too low.
Less Common Causes
- Stuck EGR valve: A valve stuck fully closed or fully open can confuse the ECU, though this more often triggers other EGR flow codes.
- ECU/PCM internal fault: Rare, but a failing driver circuit or internal short in the ECU can misread the sensor signal.
- Aftermarket modifications: EGR delete kits, poorly installed performance parts, or incorrect tuning can cause EGR-related codes, including P0405.
- Previous wiring repairs: Poorly done splices, crimp connectors, or non-sealed repairs can corrode and drag the signal low over time.
Diagnosis: Step-by-Step Guide
Tools you’ll want: A basic OBD-II scan tool (preferably one that reads live data and Mode $06), a digital multimeter (DMM), basic hand tools, and contact cleaner. A wiring diagram for your specific vehicle is very helpful.
- Confirm the code: Use your scan tool to verify P0405 is present. Check for other EGR or sensor-related codes (like P0401, P0404, etc.), as they can provide clues.
- Check freeze frame data: Look at engine load, RPM, and temperature when the code set. This helps you know under what conditions the fault occurs.
- Visual inspection: Locate the EGR valve and its connector. Look for broken wires, rubbed insulation, oil-soaked harnesses, or loose connectors. Repair obvious issues first.
- Inspect and clean the connector: Unplug the EGR connector and check for green corrosion, bent pins, or moisture. Clean with electrical contact cleaner and reconnect firmly.
- Check reference voltage and ground: With the key on (engine off), use your multimeter to verify you have a proper 5V reference and good ground at the EGR connector, following your wiring diagram.
- Measure EGR signal voltage: Back-probe the signal wire with the key on. A typical sensor will show around 0.5–1.0V closed and higher as the valve opens. If it’s stuck near 0V, you have a low circuit condition.
- Command the EGR with a scan tool: If your tool supports bi-directional control, command the EGR open and watch the signal voltage and EGR position PID. No change usually points to a bad valve/sensor or wiring.
- Wiggle test the harness: While watching live data, gently move the harness and connector. If the signal jumps or drops, there’s an intermittent wiring or connector fault.
- Check continuity to the ECU: If voltage and ground are good at the connector but the signal is wrong, test continuity of the signal wire between the EGR and ECU. Repair any high resistance or open circuits.
- Evaluate for ECU issues: Only after confirming the EGR valve and wiring are good should you suspect the ECU. This is rare and usually verified by advanced testing or substitution.
Pro tip: On some vehicles, you can compare EGR position data to Mode $06 test results. If the EGR monitor repeatedly fails while the sensor voltage stays pinned low, you almost always have a sensor or wiring problem, not a carbon blockage.
Possible Fixes & Repair Costs
Once you’ve pinpointed the cause of P0405, repairs are usually straightforward. Common fixes include replacing the EGR valve (especially if the position sensor is built in), repairing or replacing damaged wiring, cleaning or replacing the EGR connector, and in rare cases, repairing ECU circuits or reflashing the ECU.
Typical repair costs vary widely by vehicle and labor rates. A basic wiring repair or connector cleaning might run $50–$150. An EGR valve replacement usually falls in the $200–$600 range parts and labor, depending on how buried the valve is and whether OEM parts are used. ECU-related repairs or replacement can exceed $600–$1,200. Factors that affect cost include vehicle make, engine layout, parts availability, and shop labor rates in your area.
Can I Still Drive With P0405?
In most cases, you can still drive with a P0405 code without immediate danger to the engine. The car will usually go into a default EGR strategy, which may slightly affect performance and fuel economy. However, the check engine light will stay on, and you’ll likely fail an emissions or inspection test until it’s fixed.
If you notice severe rough running, stalling, or knocking, you should avoid driving and address the issue right away. Even if the car seems fine, it’s best not to ignore EGR problems for long, as they can contribute to carbon buildup and other drivability issues over time.
What Happens If You Ignore P0405?
If you ignore P0405, the main consequences are long-term: increased emissions, possible carbon buildup in the intake and valves, and a guaranteed emissions test failure. Over time, this can lead to more expensive repairs and make it harder to spot new problems because your check engine light is already on.
Related Codes
- P0474 – Exhaust Pressure Sensor Intermittent
- P0473 – Exhaust Pressure Sensor High
- P0472 – Exhaust Pressure Sensor Low
- P0471 – Exhaust Pressure Sensor Range/Performance
- P0470 – Exhaust Pressure Sensor
- P0469 – EVAP Purge Flow Sensor Circuit Intermittent
- P0468 – EVAP Purge Flow Sensor Circuit High
- P0467 – EVAP Purge Flow Sensor Circuit Low
- P0466 – EVAP Purge Flow Sensor Circuit Range/Performance
- P0465 – EVAP Purge Flow Sensor Circuit
Key Takeaways
- P0405 means the ECU sees a low signal from the EGR position sensor circuit.
- Most issues come from a bad EGR valve/sensor, wiring problems, or corroded connectors.
- Symptoms range from just a check engine light to rough idle and poor fuel economy.
- Proper diagnosis with a scan tool and multimeter prevents unnecessary parts replacement.
- Repairs often cost between $50 and $600, depending on whether it’s wiring or the EGR valve itself.
- Driving is usually possible, but ignoring the code can cause emissions failures and long-term buildup.
Vehicles Commonly Affected by P0405
P0405 shows up across many brands because almost all modern engines use some form of EGR. It’s especially common on:
- Ford: Focus, F-150, Escape, Explorer, and older modular V6/V8 engines.
- Chevrolet/GMC: Silverado, Tahoe, Impala, Malibu, and various 4.3L, 5.3L, and 6.0L engines.
- Chrysler/Dodge/Jeep: Minivans, Ram trucks, and Jeep SUVs with 3.7L, 4.7L, and 5.7L engines.
- Toyota/Lexus: Some 4-cylinder and V6 models, especially older high-mileage vehicles.
- Honda/Acura: Certain Accord, Civic, and CR-V models with known EGR and wiring issues.
- Volkswagen/Audi: TDI diesels and some gas engines with electronically controlled EGR systems.
FAQ
Can I clear P0405 and keep driving without fixing it?
You can clear the code, and it may stay off for a short time, but if the underlying problem remains, P0405 will come back. Driving without fixing it can lead to emissions test failures and may mask new problems because the check engine light is already on.
Is P0405 always caused by a bad EGR valve?
No, not always. While a faulty EGR valve with an integrated sensor is common, wiring issues, poor grounds, corroded connectors, or even ECU faults can all trigger P0405. That’s why basic electrical testing is important before replacing parts.
How serious is a P0405 code?
P0405 is usually a low to moderate severity code. Your engine is unlikely to suffer immediate damage, but it will increase emissions and may cause drivability issues in some vehicles. It should be diagnosed and repaired, but it’s not typically a “park it now” situation.
Can a dirty EGR valve cause P0405?
A dirty or carboned-up EGR valve more commonly causes flow-related codes like P0401 or P0402. However, if the buildup affects the internal position sensor or causes the valve to stick in a way that confuses the sensor, it can contribute to P0405. Cleaning sometimes helps, but a worn sensor usually requires replacement.
Do I need a professional mechanic to fix P0405?
If you’re comfortable using a multimeter and a scan tool, you can often diagnose and even fix P0405 at home, especially if it’s just a wiring or connector issue. However, if testing points to ECU faults, complex wiring problems, or you’re unsure of the results, a professional mechanic with factory-level diagnostics is a smart choice.