P0407 is an OBD-II trouble code that points to a problem in your vehicle’s Exhaust Gas Recirculation (EGR) system, specifically a “low signal” from the EGR sensor circuit B. In simple terms, your engine computer is seeing a voltage reading that’s too low from one of the EGR position/pressure sensors. That can trigger the check engine light, affect emissions, and sometimes cause drivability issues. The good news is this code is usually fixable with basic testing and some targeted parts replacement, not a full engine teardown.
What Does P0407 Mean?
P0407 stands for “Exhaust Gas Recirculation Sensor B Circuit Low.” Your ECU monitors the EGR system using one or more sensors. When the signal on the “B” circuit drops below the expected voltage range, the ECU flags this code. It’s an electrical or feedback issue, not just a stuck valve.
Depending on the vehicle, “Sensor B” may refer to a second EGR position sensor, a second circuit in the same sensor, or an EGR pressure/DPFE sensor. The underlying theme is the same: the ECU doesn’t trust the EGR feedback signal because it’s too low.
Quick Reference
- Code: P0407 – EGR Sensor B Circuit Low
- System: Exhaust Gas Recirculation (EGR)
- Severity: Low to moderate (emissions and drivability)
- Typical causes: Bad EGR sensor, wiring issues, dirty or stuck EGR valve
- Common repairs: EGR sensor/valve replacement, wiring repair, carbon cleaning
Real-World Example / Field Notes
In the shop, I see P0407 most often on higher-mileage vehicles that have spent years in stop-and-go traffic. A typical case: a mid-2000s sedan comes in with a check engine light and rough idle when warm. Scan shows P0407 stored, sometimes with an EGR flow code. A quick visual inspection reveals a cracked EGR sensor connector and heavy carbon buildup in the EGR passages. After repairing the connector, cleaning the EGR ports, and clearing the code, the car runs smoother and the light stays off. The key is checking the sensor signal before throwing parts at it.
Symptoms of P0407
- Check engine light on: The most common and sometimes only symptom you notice.
- Rough idle: Engine may idle unevenly, especially when warm or when EGR is commanded.
- Hesitation or stumble: Light throttle acceleration can feel jerky or weak.
- Reduced fuel economy: Incorrect EGR operation can slightly lower MPG.
- Failed emissions test: Elevated NOx emissions or readiness monitors not setting.
- Occasional stalling: In more severe cases, the engine can stall coming to a stop.
- Other EGR-related codes: You may also see EGR flow or range/performance codes stored.
Common Causes of P0407
Most Common Causes
- Faulty EGR position/pressure sensor: Internal failure causes a consistently low voltage signal back to the ECU.
- Damaged wiring or connector: Corroded, broken, or shorted wires in the EGR sensor “B” circuit can pull the signal low.
- Dirty or sticking EGR valve: Heavy carbon buildup can affect sensor readings or valve movement, confusing the ECU.
- Poor electrical ground: A bad ground path for the EGR sensor can result in a low reference signal.
Less Common Causes
- ECU/PCM internal fault: Rare, but a failing driver or internal circuit can misread the sensor signal.
- Incorrect or low system voltage: Charging system issues or weak battery can skew sensor readings.
- Aftermarket modifications: EGR block-off plates, incorrect tunes, or deleted systems can confuse the ECU’s EGR monitoring.
- Vacuum-related issues (older designs): On vacuum-operated EGR systems, leaks or faulty solenoids can lead to abnormal sensor feedback.
Diagnosis: Step-by-Step Guide
To diagnose P0407 properly, you’ll want a basic scan tool (preferably one that shows live data and Mode $06), a digital multimeter, and some simple hand tools. Access to a wiring diagram for your specific vehicle is extremely helpful. If you’re not comfortable with electrical testing, this is where a professional shop can save you time and money.
- Confirm the code and check for companions. Scan for all stored and pending DTCs. Note any other EGR or voltage-related codes (like P0405, P0406, P0401). Clear the codes and see if P0407 returns quickly.
- Perform a visual inspection. With the engine off, locate the EGR valve and EGR sensor/DPFE sensor. Look for cracked connectors, rubbed-through wiring, broken clips, or obvious corrosion. Fix anything obvious first.
- Check live data for EGR sensor B. On your scan tool, monitor the EGR position or pressure sensor “B” parameter. Compare the reading with key on/engine off and engine idling. A flatlined low value (often near 0 V or 0%) is a red flag.
- Test reference voltage and ground. Using a multimeter, back-probe the EGR sensor connector. You should typically see a 5V reference and a solid ground. If 5V or ground is missing, trace back through the harness and related fuses.
- Measure the signal wire. With the connector plugged in and key on, measure the signal wire voltage. On many systems, it should be somewhere between about 0.5–4.5V depending on valve position. A stuck low reading points to a bad sensor, short to ground, or ECU issue.
- Wiggle test the harness. While watching the signal on the scan tool or meter, gently move the wiring harness and connector. If the signal jumps or drops, you’ve likely got an intermittent wiring or connector fault.
- Inspect and clean the EGR valve and passages. Remove the EGR valve if accessible. Check for heavy carbon deposits. Clean the valve and intake passages with appropriate EGR/throttle body cleaner, making sure the valve can move freely.
- Check Mode $06 (if available). Some scan tools show EGR monitor test results. This can confirm if the ECU is repeatedly failing the EGR sensor test even when the valve appears to work.
- Substitute or bench-test the sensor. If wiring checks out and power/ground are good, the sensor itself is the prime suspect. On some models you can bench-test resistance or output; on others, replacement is the most practical test.
- Evaluate ECU only after all else. If a known-good sensor and wiring still produce a low signal, an ECU fault is possible but rare. At this point, professional diagnosis is recommended before replacing the ECU.
Pro tip: Always clear the code and perform a proper drive cycle after repairs. Many EGR-related monitors only run under specific conditions (warm engine, steady cruise), so a quick spin around the block may not be enough to confirm the fix.
Possible Fixes & Repair Costs
Most P0407 repairs are straightforward once you pinpoint the cause. Common fixes include replacing the EGR position or DPFE sensor, repairing or replacing damaged wiring/connectors, cleaning or replacing the EGR valve, and in rare cases addressing ECU faults. At a typical shop, you can expect costs in the range of about $100–$250 for sensor replacement, $150–$400 for EGR valve replacement, and $100–$250 for wiring repairs, depending on labor rates, parts brand, and how buried the components are on your particular engine.
Can I Still Drive With P0407?
In most cases, you can still drive with P0407 without immediate engine damage, especially if the only symptom is a check engine light. However, the EGR system plays an important role in controlling combustion temperatures and NOx emissions. Driving long-term with a faulty EGR sensor can lead to higher emissions, possible pinging under load, and a failed inspection. If drivability issues like stalling, rough running, or hesitation are present, you should treat the repair as more urgent and avoid long trips until it’s fixed.
What Happens If You Ignore P0407?
If you ignore P0407, you risk long-term issues like carbon buildup in the intake, higher combustion temperatures, and potential damage to emission components. You’ll almost certainly fail an emissions or smog test, and the check engine light will mask new codes that might appear later. Fixing the problem sooner keeps the engine running cleaner and saves you from chasing multiple issues down the road.
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
- P0407 means the ECU sees a low signal from the EGR sensor “B” circuit, usually an electrical or sensor issue.
- Common causes include a bad EGR sensor, wiring/connector problems, and carbon buildup affecting valve operation.
- Symptoms range from just a check engine light to rough idle, hesitation, and failed emissions tests.
- Diagnosis involves checking live data, verifying power/ground, testing the signal wire, and inspecting the EGR valve and passages.
- Repairs are typically moderate in cost and well within the abilities of a good DIYer with a scan tool and multimeter.
Vehicles Commonly Affected by P0407
P0407 shows up across many makes, but it’s especially common on certain domestic and Asian vehicles. You’ll often see it on Chrysler, Dodge, and Jeep models with electronic EGR valves, as well as various Ford cars and trucks that use DPFE-style EGR sensors. Many GM vehicles (Chevrolet, GMC, Buick) with higher mileage can also trigger this code when the EGR sensor or wiring starts to fail. Among imports, some Hyundai, Kia, and Volkswagen models will log P0407 when their EGR feedback circuits get dirty or corroded.
FAQ
Can I clear P0407 and keep driving without fixing it?
You can clear the code, but it will usually come back if the underlying problem isn’t fixed. The ECU continuously monitors the EGR sensor, so as soon as it sees the low signal again, the check engine light will return. Clearing the code is fine for testing, but it’s not a long-term solution.
Is P0407 an EGR valve problem or a sensor problem?
P0407 specifically points to a low signal from the EGR sensor “B” circuit, so it’s more of a sensor or wiring issue than a valve-only problem. However, a badly sticking or carboned-up EGR valve can affect sensor readings. That’s why you should inspect both the sensor circuit and the valve during diagnosis.
How do I know if the EGR sensor is bad or the wiring is the issue?
You’ll need to test for proper 5V reference, ground, and signal voltage at the sensor connector. If power and ground are good but the signal stays low even when you move or substitute the sensor, wiring or ECU may be at fault. If a new or known-good sensor restores a normal signal, the original sensor was the problem.
Can P0407 cause my car to fail an emissions or smog test?
Yes. A stored P0407 code will usually cause an automatic failure in OBD-based emissions testing, even if the car seems to run fine. The EGR monitor may not set to “ready,” and NOx emissions can be higher than allowed. Fixing the issue and completing a proper drive cycle before your test is important.
Does P0407 always require replacing parts?
Not always. Sometimes the fix is as simple as cleaning a corroded connector, repairing a damaged wire, or cleaning a carboned-up EGR valve and passages. Parts replacement is common for failed sensors or valves, but you should always diagnose first instead of guessing and swapping components.