If you’re seeing code P0474 on your scanner, your vehicle is telling you there’s an intermittent or erratic signal from the exhaust back pressure sensor circuit. This code shows up a lot on turbo diesels, but some gas engines use similar logic. While it doesn’t always mean major engine damage, it can affect drivability, turbo performance, and fuel economy if you ignore it. In this guide, you’ll learn what P0474 means, common causes, symptoms, and how you or your mechanic can diagnose and fix it correctly.
What Does P0474 Mean?
P0474 is an OBD-II diagnostic trouble code that stands for “Exhaust Pressure Sensor ‘A’ Circuit Intermittent.” In simple terms, your ECU is seeing a back pressure sensor signal that jumps around, drops out, or doesn’t match what it expects under certain conditions.
The exhaust back pressure sensor helps the ECU control turbo boost, EGR (exhaust gas recirculation), and sometimes DPF (diesel particulate filter) regeneration. When the signal is unstable, the ECU can’t trust the data, so it sets P0474 and often goes into a reduced power or backup strategy to protect the engine and emissions system.
Quick Reference
- Code: P0474 – Exhaust Pressure Sensor “A” Circuit Intermittent
- Severity: Moderate – can affect power and emissions
- Common on: Turbo diesels (Ford Powerstroke, Ram Cummins, some Mercedes, VW, etc.)
- Typical causes: Faulty sensor, wiring issues, clogged sensor tube, corrosion
- Risk: Poor performance, higher soot buildup, possible DPF issues if ignored
Real-World Example / Field Notes
In the shop, I see P0474 most often on Ford Powerstroke and Ram Cummins trucks. A common pattern: the truck comes in with low power under load, sometimes a rough shift, and the owner says it feels “like the turbo is lazy.” The scan tool shows P0474 along with occasional EGR or turbo codes. Many times the exhaust back pressure sensor tube is plugged with soot, or the sensor connector is green with corrosion. Clean the tube, replace the sensor, repair the wiring, clear the codes, and the truck comes back to life.
Symptoms of P0474
- Check engine light on: MIL illuminated, sometimes with other turbo or EGR codes.
- Reduced power: Noticeable loss of acceleration, especially when towing or climbing hills.
- Poor fuel economy: More fuel used than normal due to incorrect boost/EGR control.
- Rough or inconsistent shifting: On some automatics, erratic load data can affect shift timing.
- Turbo lag or flat feel: Turbo may not spool properly or feels inconsistent.
- Excessive smoke: Black or dark smoke on diesels under load if fueling and air don’t match.
- DPF or EGR issues: Regens may be more frequent or incomplete, and EGR performance can suffer.
Common Causes of P0474
Most Common Causes
- Faulty exhaust back pressure sensor: Internal failure, contamination, or age causes erratic voltage output.
- Clogged sensor tube or port: Soot and carbon plug the small passage between exhaust and sensor, causing unstable readings.
- Damaged wiring or connector: Chafed wires, broken insulation, or loose/oxidized pins create intermittent signal loss.
- Moisture intrusion: Water or oil in the connector causes corrosion and unstable voltage.
- Previous poor-quality repairs: Incorrect splices, cheap connectors, or misrouted harnesses leading to intermittent opens/shorts.
Less Common Causes
- ECU/PCM internal fault: Rare, but possible if all wiring and sensor tests pass and other codes are present.
- Exhaust leaks near sensor port: Leaks can disturb pressure readings and sensor response.
- Aftermarket modifications: Tuners, deleted EGR/DPF, or custom exhausts can confuse the ECU’s expected pressure values.
- Ground or power supply issues: Shared grounds or reference voltage problems affecting multiple sensors.
- Severe turbo or EGR malfunction: Unusual pressure behavior that the ECU interprets as an intermittent sensor signal.
Diagnosis: Step-by-Step Guide
To properly diagnose P0474, you’ll want a quality scan tool (preferably with live data and Mode $06 access), a digital multimeter, basic hand tools, and possibly a wiring diagram for your specific vehicle. A smoke machine and lab scope are helpful but not mandatory for most DIYers.
- Confirm the code and check for companions: Scan the vehicle and note all stored and pending codes. If you see related EGR, turbo, or DPF codes, they may point to a shared root cause.
- Inspect the exhaust back pressure sensor and tubing: Locate the sensor (often on or near the exhaust manifold or up-pipe). Check the metal tube or port for heavy soot buildup, cracks, or disconnection.
- Check the sensor connector: Look for corrosion, bent pins, loose fit, or signs of moisture. Gently tug each wire to ensure it’s firmly crimped.
- Visual inspection of wiring harness: Follow the harness from the sensor toward the ECU. Look for rubbing on brackets, heat damage from the exhaust, or previous repairs.
- Test sensor power and ground: With the key on, use a multimeter to verify 5V reference (if applicable), proper ground, and signal wire continuity according to the wiring diagram.
- Monitor live data: On your scan tool, watch the exhaust back pressure reading at idle and while gently revving. Compare it to barometric pressure and boost (if available). Intermittent spikes or dropouts suggest sensor or wiring issues.
- Check Mode $06 and freeze frame: Mode $06 can show test results for the sensor circuit, and freeze frame data tells you under what conditions P0474 set (RPM, load, temperature). This helps you reproduce the fault.
- Clean or replace the sensor and tube: If the tube is clogged, remove and clean it with carb cleaner or a small brush. If the sensor is contaminated or fails voltage tests, replace it with a quality OEM or equivalent part.
- Perform a wiggle test: With the engine running and live data displayed, gently move the harness and connector. If the reading jumps or the engine stumbles, you’ve found a wiring or connector issue.
- Clear codes and road test: After repairs, clear the DTCs and perform a road test under similar conditions to the freeze frame. Re-scan to confirm P0474 does not return.
Pro tip: On many diesel trucks, cleaning or replacing the exhaust back pressure sensor tube is just as important as replacing the sensor itself. A brand-new sensor on a plugged tube will still give you bad data and recurring codes.
Possible Fixes & Repair Costs
Most P0474 repairs are straightforward once you identify the cause. Common fixes include cleaning or replacing the exhaust back pressure sensor tube, replacing the sensor, repairing damaged wiring, or cleaning and resealing connectors. In more stubborn cases, you might need ECU reprogramming or, very rarely, ECU replacement.
Typical repair costs at a shop can range from about $100–$200 for cleaning and basic wiring repair, $200–$450 for sensor and tube replacement, and $500+ if extensive wiring harness work or ECU diagnosis is needed. Costs vary based on vehicle make, parts quality (OEM vs aftermarket), labor rates in your area, and how hard the sensor is to access.
Can I Still Drive With P0474?
You can usually drive with P0474 for a short period, but it’s not ideal to ignore it. Many vehicles will default to a backup strategy that limits turbo performance to protect the engine and emissions system. That means less power, potential for higher soot buildup, and possible side effects on EGR and DPF operation. If you notice severe loss of power, heavy smoke, or additional warning lights, you should avoid towing or highway passing and get it checked as soon as possible.
What Happens If You Ignore P0474?
If you ignore P0474 long-term, the ECU continues to operate with unreliable exhaust pressure data. That can accelerate soot buildup in the EGR system and DPF, increase regeneration frequency, and potentially lead to expensive components plugging up or failing. You may also see more related codes over time, and what started as a simple sensor or wiring issue can snowball into a bigger repair bill.
Related Codes
- 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
- P0464 – Fuel Level Sensor “A” Circuit Intermittent
Key Takeaways
- P0474 means the exhaust back pressure sensor signal is intermittent or erratic, not just out of range.
- The code is common on turbo diesels and can affect turbo, EGR, and DPF performance.
- Most issues trace back to a bad sensor, clogged sensor tube, or wiring/connector problems.
- Diagnosis should include visual inspection, live data monitoring, and basic electrical tests.
- Fixes are often affordable if handled early, before soot and heat cause secondary damage.
Vehicles Commonly Affected by P0474
P0474 is especially common on modern diesel trucks and SUVs that rely heavily on exhaust pressure data. You’ll often see it on:
- Ford: Powerstroke 6.0L, 6.4L, 6.7L in F-250, F-350, and larger trucks.
- Ram: Cummins-equipped 2500 and 3500 models.
- GM: Some Duramax diesel applications.
- Mercedes-Benz and Sprinter vans: Diesel engines with DPF and EGR systems.
- Volkswagen/Audi: Certain TDI engines using exhaust pressure feedback.
- Other turbo diesels: Including some Asian and European light-duty trucks and SUVs.
Gasoline turbo engines that use exhaust pressure feedback can also set P0474, but it’s far more frequently seen on diesel platforms with complex emissions systems.
FAQ
Can I clear P0474 and keep driving if the truck feels fine?
You can clear the code, but if the underlying issue is still there, P0474 will usually return. Even if the truck feels okay now, incorrect exhaust pressure data can slowly cause soot buildup and emissions problems. It’s better to diagnose and fix the cause instead of repeatedly clearing the code.
Is P0474 always caused by a bad exhaust back pressure sensor?
No. The sensor is a common failure point, but wiring issues, clogged sensor tubes, and connector corrosion are just as frequent. Replacing the sensor without checking the tube and wiring can waste money and leave the problem unsolved.
How do I know if the exhaust back pressure sensor tube is clogged?
Remove the tube from the sensor and exhaust port and try blowing through it. If it’s difficult or impossible, it’s restricted with soot. Often you’ll see heavy carbon buildup at the ends. Cleaning or replacing the tube is a simple and effective fix in many P0474 cases.
Can a tuner or deleted emissions system cause P0474?
Yes, aftermarket tuning, EGR/DPF deletes, or custom exhaust work can change exhaust pressure behavior beyond what the ECU expects. That can trigger P0474 and related codes, especially if the tune isn’t properly calibrated for the hardware changes.
How urgent is it to fix P0474 on a diesel truck I use for towing?
If you tow regularly, you should address P0474 as soon as possible. Under heavy load, the engine and turbo rely on accurate exhaust pressure data for safe operation. Ignoring the code while towing can increase exhaust temps, soot buildup, and stress on the turbo and DPF, leading to more expensive repairs down the road.