OBD-II trouble code
P0473: Exhaust Pressure Sensor 'A' Circuit High Input
The exhaust pressure signal is above the range the module accepts. Before assuming the sensor is lying, consider that it might be telling the truth — a crushed pipe or a plugged filter really does produce extreme back pressure, and that possibility changes the whole diagnosis.
Quick facts
- System
- Powertrain
- Category
- Exhaust / Aftertreatment
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $90 – $3,200
- DIY difficulty
- Intermediate DIY
What does P0473 mean?
Most high-input circuit codes are safe to treat as fiction. A coolant temperature sensor reporting an impossible value is not describing anything real; it is describing a wiring fault. Exhaust pressure is different, and that difference is the single most useful thing to know about P0473. Exhaust systems genuinely can develop pressures far outside the normal operating band. A catalyst substrate that has broken up and packed itself into the pipe, a particulate filter loaded past the point of clearing, an exhaust flattened by a kerb strike or a jack pad, a collapsed flexible section, even ice in a tailpipe on some vehicles — all of these produce very high back pressure. A sensor reading it is not malfunctioning. It is doing exactly what it was fitted to do, and replacing it will change nothing except the invoice.
So the first question on this code is not 'which wire is shorted' but 'is this reading plausible?' That question has a physical answer. Back pressure can be measured directly: remove the sensor's pressure tube at the exhaust tapping, thread in a mechanical gauge, and read what the engine is actually producing at idle and at raised rpm. Most engines sit in low single-digit psi at idle and stay modest even under load. A gauge that agrees with the sensor means the exhaust is genuinely restricted and the diagnosis moves downstream into the pipe, the catalyst or the filter. A gauge that shows normal pressure while the sensor reports extremes condemns the sensor or its circuit and lets you stop worrying about the exhaust. That is a decisive fork available for the price of a gauge, and skipping it is how a restricted exhaust ends up with three sensors fitted to it.
When the reading is not real, the electrical mechanisms are the familiar ones with an exhaust-specific twist. A signal wire touching a source of voltage will drive the input high, and on this circuit the most likely source is not a random power feed but the sensor's own five-volt reference lying alongside it in the same connector and the same loom. Water and corrosion inside a connector bridge adjacent terminals long before they bridge anything else, so a green, salt-crusted plug in road-spray territory is a classic P0473. The other mechanism is a compromised ground. This sensor's ground path frequently terminates at a stud on the block or a bracket in the same wet, hot region, and a ring terminal that has corroded under its washer raises the sensor's reference point without any short existing at all. Nothing is touching power; the whole sensor has simply floated upward. Chasing a short in that situation finds nothing, which is why the ground should be measured for voltage drop rather than merely checked for continuity.
The practical urgency depends on which answer you get. A wiring or sensor fault means the module has lost an input it uses for DPF soot estimation, EGR flow and, on variable geometry turbochargers, vane control — annoying, power-limiting, and worth fixing before regeneration strategy drifts. A genuinely restricted exhaust is a different matter. A severely blocked exhaust chokes the engine, drives exhaust gas temperatures up, loads the turbocharger's bearings and can make a vehicle undriveable within a short distance. If the gauge confirms real restriction, the code is a warning about the exhaust rather than a complaint about a sensor, and continuing to drive is the wrong response.
Common causes
- Genuinely restricted exhaust — a broken-up catalyst substrate, a fully loaded particulate filter, a crushed pipe or a collapsed flexible section — reported accurately by a healthy sensor
- Signal wire shorted to the sensor's own five-volt reference through a water-contaminated or corroded connector
- Corroded or high-resistance sensor ground, which raises the whole signal without any short being present
- Signal wire shorted to another voltage source where insulation has been heat-embrittled near the turbocharger or exhaust
- Failed transducer stuck at the top of its output range
- Open in the sensor ground circuit, which on many designs drives the reading to maximum
- Water inside the sensor body itself after the pressure tube has drawn in condensate
- Incorrect or non-equivalent replacement sensor fitted, with a different output range to the one the calibration expects
Symptoms
- Check engine light with P0473 stored
- Noticeably reduced power, and on a truly restricted exhaust an engine that will barely pull away
- Excessive heat from the exhaust or a smell of hot metal, when the restriction is real
- Regeneration cycles that run repeatedly or run for unusually long periods
- Rough idle or stalling on severe restriction as the engine struggles to expel exhaust
- Live data showing exhaust pressure far above plausible values, including with the engine switched off
- Boost that builds slowly or overshoots on variable geometry turbocharger applications
- Accompanying DPF, catalyst efficiency or turbocharger underboost codes
Diagnostic steps
- 1.Before anything electrical, ask whether the reading could be true. Note whether the vehicle also feels choked, hot or slow to rev, which is what a real restriction feels like.
- 2.Measure back pressure mechanically. Remove the pressure tube at the exhaust tapping, fit a back pressure gauge and read the value at idle and at raised rpm, then compare it with what the sensor is reporting.
- 3.If the gauge agrees with the sensor, stop diagnosing the sensor and inspect the exhaust — tap along the pipe for a rattling catalyst substrate, check for physical crush damage and assess particulate filter loading.
- 4.If the gauge disagrees, compare the sensor reading against barometric pressure with the engine off and the key on, where the exhaust must be at atmospheric and the two values should match closely.
- 5.Unplug the sensor connector with the key on. On a pulled-up input the reading normally goes to maximum when disconnected, so a value that stays high proves nothing while a value that changes tells you the module is responding to the sensor.
- 6.Inspect the connector closely for moisture, salt and green corrosion bridging the signal and reference terminals, which is the most common way this circuit is driven high.
- 7.Measure voltage drop on the sensor ground with the engine running rather than checking continuity with the key off, since a corroded ring terminal can show continuity and still raise the signal.
- 8.Check the signal wire for a short to the five-volt reference by disconnecting both ends and measuring resistance between them.
- 9.Examine the loom around the turbocharger and exhaust for insulation that has hardened, flattened or split from heat, which is where this circuit picks up voltage.
- 10.If a sensor was fitted previously, confirm it is the correct part number for the application, because a substituted sensor with a different pressure range reads high across the board.
Repair cost
$90 – $3,200
The spread here is unusually wide because the code has two entirely different answers. If the sensor is lying, it is ordinary work: $90 to $170 for diagnosis, $80 to $250 to repair a corroded connector or a shorted section of harness, or $180 to $400 for a sensor replacement including labour. Cleaning and re-terminating a corroded ground stud is often under $120. If the sensor is telling the truth, the cost belongs to the exhaust: a collapsed flexible section or a crushed pipe section is $150 to $600, a failed catalytic converter is $600 to $2,000, and a particulate filter that can no longer be regenerated is $1,000 to $3,000 replaced, or $400 to $900 for a professional off-vehicle clean where that is offered. Spending the price of a back pressure gauge first is what decides which of these two you are in.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with exhaust back pressure sensor / tube replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.