OBD-II trouble code
P0470: Exhaust Pressure Sensor 'A' Circuit Malfunction
The module cannot get a usable exhaust pressure reading. The sensor itself rarely fails — what fails is the little steel tube that carries pressure from the exhaust to it, and it fails by filling with soot, which is a job you can often clear rather than replace.
Quick facts
- System
- Powertrain
- Category
- Exhaust / Aftertreatment
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $90 – $550
- DIY difficulty
- Intermediate DIY
What does P0470 mean?
Exhaust pressure is one of the more useful numbers a modern engine can measure, and one of the hardest to measure. The gas in an exhaust system runs at temperatures that would destroy any pressure transducer within minutes, so engineers do not put the sensor in the exhaust. They mount the transducer somewhere cool — usually bolted to a bracket on the engine, the bulkhead or an inner wing — and connect it to a tapping in the exhaust with a small-bore steel tube. Pressure travels up that tube; the hot gas, in principle, stays where it is.
In practice, of course, the gas does creep up the tube, cools as it goes, and leaves what it was carrying behind. On a diesel that means soot. Over tens of thousands of miles the bore narrows, and eventually a tube designed to transmit pressure instantly transmits it slowly, or not at all. This single mechanism accounts for a very large share of exhaust pressure sensor faults, and it has an important consequence for anyone paying the bill: the failure is frequently a blocked tube rather than a broken sensor, and a blocked tube can often be cleared with a length of stiff wire, a suitable drill bit turned by hand and some carburettor cleaner. The part cost in that scenario is nothing. Anyone quoting a sensor before they have checked whether the tube is clear has skipped the cheapest and most likely repair.
What the reading is used for explains why this code matters more than an EVAP fault. On a diesel, exhaust back pressure is central to three systems. It is one of the inputs used to estimate how much soot the diesel particulate filter is holding, and therefore when to run a regeneration. It informs EGR flow control, because the pressure difference across the EGR path is what determines how much exhaust actually recirculates. And on engines with variable geometry turbochargers it feeds boost and vane control. Take that reading away and the module has to fall back on defaults, which is why the practical symptoms are power-related rather than emissions-related: reduced power or a limp mode, a refusal to start or complete a regeneration, and sometimes a rough or unsettled idle as EGR control loses its bearings.
There is a caveat worth stating plainly. This is predominantly a diesel code. It appears on turbodiesels with DPFs and EGR most of all, and on some petrol applications with exhaust pressure monitoring, but several manufacturers use P0470 with a make-specific meaning, and the number of exhaust pressure sensors fitted varies — 'A' implies there may be a 'B', and on a vehicle with sensors both upstream and downstream of the DPF, identifying which physical sensor is 'A' is the first thing to establish rather than something to assume. Check the service information for the exact engine before ordering anything.
The electrical side is ordinary three-wire sensor work: a five-volt reference, a ground, and a signal that rises with pressure. What is not ordinary is the environment. The tube and the sensor's mounting live in road-spray territory, so corrosion at the tube's threaded fitting is common and a seized fitting can turn a ten-minute job into an hour of heat and penetrating oil. It is also worth checking the tube for cracks and for a fractured joint at the exhaust tapping, since a leak there gives a low reading without anything electrical being wrong at all.
The reason to attend to this promptly is not that the vehicle will fail tomorrow. It is that the DPF depends on this reading. A module that cannot estimate soot loading cannot manage regeneration properly, and a DPF allowed to fill beyond a certain point can no longer be cleared by a normal regeneration cycle. That is the difference between a cheap repair and a four-figure one, and it is the entire argument for not ignoring this code for months.
Common causes
- Pressure tube between the exhaust tapping and the sensor blocked with soot, which is the single most common cause and often clearable rather than requiring parts
- Cracked, split or fractured pressure tube giving a false low reading with no electrical fault present
- Corroded or seized threaded fitting at the exhaust tapping, sometimes leaking as well as being difficult to remove
- Failed pressure transducer, usually after long service in a road-spray environment
- Corroded connector at the sensor, where moisture has tracked into the terminals
- Damaged or chafed wiring where the harness runs along the engine or bulkhead near hot components
- Loss of the shared five-volt reference, which affects this sensor along with others on the same rail
- Sensor incorrectly identified during a previous repair on engines fitted with more than one exhaust pressure sensor
Symptoms
- Check engine light with P0470 stored
- Reduced power or a limp mode, particularly under load or on a gradient
- DPF regeneration failing to start or failing to complete, sometimes with a separate DPF warning
- Rough or unsettled idle as EGR control loses a key input
- Boost that feels flat or inconsistent on engines with a variable geometry turbocharger
- Increased fuel consumption over time as regenerations become unreliable
- Additional DPF, EGR or boost codes stored alongside this one
Diagnostic steps
- 1.Locate the sensor and its pressure tube physically before testing anything, and confirm from service information which sensor is 'A' on engines fitted with more than one.
- 2.Disconnect the pressure tube at the sensor and check it is clear. A tube blocked with soot is the most likely cause and the cheapest to fix, so it belongs before any electrical test.
- 3.Clear a blocked tube with stiff wire, a suitably sized drill bit turned by hand and solvent, then confirm the bore is open along its whole length rather than just at the ends.
- 4.Inspect the tube for cracks, kinks and a fractured joint at the exhaust tapping, since a leak produces a low reading with no electrical fault.
- 5.Check the threaded fitting at the exhaust for corrosion, and plan for heat and penetrating oil if it is seized rather than forcing it and snapping the tapping.
- 6.Read all stored codes together. Accompanying DPF, EGR or boost codes indicate how far the missing reading has propagated and sometimes point at the real root cause.
- 7.Back-probe the connector and verify the five-volt reference and ground with the key on before considering the sensor itself.
- 8.If the reference voltage is missing, check whether other sensors on the same rail are also reporting faults, which redirects the search to the shared supply.
- 9.Inspect the connector for moisture, corrosion and pushed-out terminals, and the harness for chafe where it passes hot components.
- 10.Compare the sensor's reading at key-on engine-off against barometric pressure, since with the engine stopped the exhaust must be at atmospheric and any large discrepancy condemns the sensor or its tube.
Repair cost
$90 – $550
The best case is genuinely close to free in parts: clearing a soot-blocked pressure tube is labour only, and most shops will do it within a single diagnostic hour, so $90 to $180 is realistic. A replacement tube or hose assembly runs $25 to $120. The sensor itself is commonly $50 to $250 depending on make, with half an hour to an hour of labour, putting a typical replacement at $180 to $400. The upper end reflects a seized or corroded fitting at the exhaust tapping, which can add an hour of heat and penetrating oil, or a broken tapping that has to be repaired. Note what is not in this range: a DPF allowed to block because soot loading could not be estimated is a $1,000 to $3,000 problem, which is the real reason not to leave this code unattended.
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.