P164B Mercedes — Causes, Fix & Cost

P164B means the ECU is detecting a performance issue with the turbocharger boost control position sensor — typically that the sensor reading does not match the commanded position or is erratic. On most Mercedes diesels, this is a sensor or actuator issue, not a failed turbocharger. It should be diagnosed cheapest-first.

Most common cause: a faulty boost control position sensor — typically £150–£350 fitted [PATTERN DATA]
Worst case: turbocharger replacement, £1,200–£1,800 fitted [PATTERN DATA]
Commonly seen alongside engine management light and limp mode
Frequently appears with P132B or P2563 — the combination narrows the diagnosis considerably

Do not let anyone sell you a new turbo before the sensor and its wiring have been inspected. Full diagnostic order below.

What P164B Actually Means

In a turbocharged Mercedes diesel, the ECU uses a position sensor on the turbocharger's VGT (variable geometry turbo) actuator to monitor the actual position of the vanes. This sensor provides feedback to the ECU, which compares it to the commanded position. P164B is set when the sensor reading is inconsistent with the commanded position — it may be lagging, sticking, or showing intermittent values. Crucially, the code describes a performance issue with the sensor or its feedback, not necessarily a mechanical problem with the turbo itself. The sensor could be faulty, the wiring could be damaged, or the actuator could be sticking. That distinction is the entire difference between a £150 sensor and a £1,500 turbo replacement. This code appears across the full range of Mercedes diesel engines, from the OM651 to the OM642, and the diagnostic approach is essentially identical regardless of which engine triggers it.

Symptoms You'll Notice Alongside It

Engine management light illuminated, usually amber
Noticeable power loss or limp mode, especially under acceleration
Hesitation or surging — the engine may feel sluggish then suddenly surge
Reduced fuel economy and black smoke from exhaust
Possible turbo whistle or unusual intake noises

Common Causes, Ranked

Ordered by how often each turns out to be the real culprit — with typical fitted cost against each, so you can sanity-check any quote you've been given.

Cause	Likelihood	Typical Cost (fitted)	Notes
Faulty boost control position sensor	Very High	£150–£350	Most common — sensor may be worn or intermittent
Wiring/connector issue (chafed, corroded, broken wire)	High	£100–£250 (repair)	Often overlooked — a simple wiring fix can resolve it
Sticking VGT actuator (mechanical resistance)	Medium	£200–£600 (cleaning or actuator replacement)	Carbon buildup can cause the actuator to stick
Boost leak affecting actuator response	Medium	£150–£400	A leak can cause erratic boost pressure, confusing the sensor feedback
Turbocharger mechanical failure (worn bearings, damaged vanes)	Low	£1,200–£1,800	Genuine turbo failure is rare — rule out sensor and wiring first

Cost figures [PATTERN DATA] — indicative independent-specialist pricing, not drawn from our engine replacement dataset.

Diagnostic Order — Cheapest First

Check live data of the position sensor

Using a diagnostic tool, compare the commanded position with the actual position sensor reading. If the sensor reading is erratic or doesn't match, it's likely faulty.

Inspect the sensor wiring and connector

Look for chafing, corrosion, or loose pins. A simple repair can resolve P164B.

Test the sensor resistance and voltage

With a multimeter, measure the sensor's reference voltage and signal output. Out-of-range readings indicate a faulty sensor.

Check VGT actuator movement

Using a vacuum pump or diagnostic tool, command the actuator to move. Watch the sensor reading — if it doesn't follow smoothly, the actuator may be sticking.

Only then consider the turbo

If sensor and actuator are working correctly, the turbo's mechanical condition may be the issue.

✓

Not sure where to start?

Our diagnostic wizard walks the same order, or confirm your engine first with the registration lookup.

Can You Still Drive It?

Conditionally, yes — short journeys, but avoid heavy acceleration. P164B on its own is not an engine-destroying fault, but it will result in reduced power and fuel economy. If the vehicle has dropped into limp mode, motorway driving is unsafe because you cannot accelerate normally. Get it looked at within a day or two, and drive gently with minimal boost demand.

Related Fault Codes

P164B rarely appears alone. Which codes accompany it materially changes the diagnosis.

P132B — Turbocharger Boost Control Performance

If you have P164B and P132B together, the sensor may be the root cause of the performance issue.

P2563 — Turbocharger Boost Control Position Sensor

Often accompanies P164B — check the sensor and wiring together.

P0299 — Turbocharger Underboost

A faulty sensor can cause incorrect boost control, leading to underboost.

Turbo whistle or siren noise

Can indicate turbo bearing wear or VNT mechanism issues. See turbocharger failure.

Frequently Asked Questions

Can I drive with P164B on a Mercedes?

Yes, for short journeys, but avoid heavy acceleration. The car will have reduced power and may go into limp mode. Get it checked within a few days.

Does P164B always mean the turbo has failed?

No. In fact, turbo failure is the least likely cause. A faulty sensor or wiring issue are far more common and much cheaper to fix.

Will clearing the code fix it?

Only temporarily. The code will return as soon as the ECU detects the position sensor performance issue again. Clearing it also destroys the freeze-frame data a specialist would use to narrow the cause.

How much should diagnosis cost?

Expect one hour of diagnostic time at an independent Mercedes specialist. Many will offset that cost against the repair if you proceed with them.

✓

Cheapest-First AlwaysWe rank causes by likelihood and cost, not by what's profitable to quote.

✓

Honest About CostWhere a fault is usually cheap to fix, we say so plainly.

✓

15+ Vetted Mercedes SpecialistsDiagnostics carried out by people who work on these daily.

✓

100% IndependentNo sponsors, no manufacturer influence.

P164B Mercedes — Turbocharger Boost Control Position Sensor Performance