P0407 is one of those diagnostic trouble codes that immediately grabs my attention, because it tells me there’s a hiccup with the Exhaust Gas Recirculation (EGR) system-specifically, we’re dealing with the "B" circuit of the EGR position sensor. The EGR system’s job is to help your engine burn cleaner by recycling a measured portion of exhaust gases right back into the combustion chamber. This keeps combustion temps down, which is key for cutting down those nasty nitrogen oxide emissions. Now, the EGR valve itself can be either electrically or vacuum controlled, and it relies on position sensors to let the PCM (that’s your car’s engine computer) know what’s happening-whether the valve is opening and closing as it should. When I see the PCM throwing a P0407, it means it’s getting a signal from the EGR position sensor "B" that’s way lower than expected. Usually, we’re looking at an electrical gremlin or a valve that’s stuck. This is almost a twin to the P0405 code, but P0407 is all about the "B" sensor circuit. Just a heads-up: where exactly the "A" and "B" sensors are located can change depending on your vehicle, so I always recommend checking your repair manual for the exact spot.
DTC P0407
4997
6 minutes of readingCauses of obd code P0407
From experience, the most common reasons for a P0407 code are electrical issues or a faulty EGR valve. Here’s what I usually find when diagnosing this code:
- A short to ground in the EGR sensor signal or reference circuits
- A short to voltage in the EGR ground or signal circuits
- A bad EGR valve (the internal sensor fails or the valve sticks)
- Wiring problems, like damaged wires or loose terminals at the PCM or EGR connector
Sometimes, moisture or carbon buildup can cause the valve to stick, especially in cold weather. I’ve also seen cases where the problem is intermittent and goes away once the engine warms up.
Symptoms of P0407 code
When this code pops up, you’ll probably notice the check engine light (MIL) is on. Most drivers don’t feel a big difference in how the car runs, but in some cases, you might notice rough idling, hesitation, or even a drop in fuel efficiency. If the EGR valve is stuck open or closed, it can cause the engine to run a bit rough or stumble, especially at idle or during acceleration. But honestly, sometimes the only clue is that warning light on your dash.
Diagnosis for P0407 engine code
Here’s how I approach a P0407 code, step by step:
- First, I always start with a visual inspection. Check the wiring and connectors at the EGR valve for any obvious damage, corrosion, or loose pins. It’s easy to overlook a broken wire or a dirty connector.
- Next, I use a scan tool to command the EGR valve open and closed while watching the feedback signal. If the valve moves and the scan tool shows the correct position, the issue might be intermittent or weather-related.
- If the valve doesn’t respond, I disconnect the EGR harness and check for the correct reference voltage (usually 5 volts) at the connector using a voltmeter. No voltage? That points to a wiring issue or a problem with the PCM.
- If there’s 12 volts where there should be 5, that means there’s a short to power in the reference circuit-something that needs to be fixed right away.
- If the reference voltage is good, I check the signal wire for shorts to ground or breaks. A test light can help here-if it lights up when it shouldn’t, you’ve found a short.
- If all the wiring checks out, but the problem remains, I recommend replacing the EGR valve itself. Sometimes the internal position sensor just fails, or the valve sticks due to carbon buildup.
It’s best to have someone help you during these tests, especially when checking live data or moving connectors around.
Common Mistakes when troubleshooting dtc P0407
One thing I see a lot is folks jumping straight to replacing the EGR valve without checking the wiring or connectors first. That’s a surefire way to waste money and time. Another common mistake is not checking for shorts to power or ground in the circuits-these can be tricky to spot if you’re not thorough. Don’t forget to inspect the PCM connector and make sure all terminals are tight and clean. Skipping these steps can lead to a misdiagnosis and more headaches down the road.
Seriousness of P0407 issues
This isn’t something you want to ignore. While the car might seem to run fine at first, a malfunctioning EGR system can lead to increased emissions and, over time, engine performance issues. If the valve sticks open, it can cause rough running and even stalling. If it’s stuck closed, you risk higher combustion temperatures, which can damage the engine or catalytic converter. Honestly, things can go south quickly if this is left unchecked. It’s always better to fix it before it leads to bigger (and more expensive) problems.
Repair steps for obd2 code P0407
Here’s what usually fixes a P0407 code, based on what I see in the shop and OEM procedures:
- Repair or replace any damaged wiring or connectors in the EGR circuit
- Clean the EGR valve if it’s sticking due to carbon buildup (sometimes a good cleaning is all it needs)
- Replace the EGR valve if the internal sensor or actuator is faulty
- Fix any shorts to ground or power in the reference or signal circuits
- In rare cases, if all else fails and there’s no reference voltage, the PCM may need to be replaced-but that’s a last resort after all other checks
Conclusion
To sum it up, P0407 means your EGR system isn’t sending the right feedback to the engine computer, usually because of an electrical issue or a faulty valve. It’s not something to put off-acting quickly can save you from bigger headaches and costly repairs. The best way forward is to start with a careful inspection of the wiring and connectors, then test the EGR valve and circuits as needed. Most of the time, the fix is straightforward once you track down the root cause. If you’re not comfortable with electrical checks, it’s wise to get help-this is one of those problems where a little attention now can prevent a lot of trouble later.
