Moderate SeveritySafe to drive (short-term)Fuel System
P0170 means the fuel trim values on bank 1 have exceeded the normal correction range. The ECU can no longer properly compensate for a rich or lean condition by adjusting fuel delivery. This indicates a persistent air-fuel mixture problem that needs investigation.
What does P0170 mean?
P0170 means the fuel trim values on bank 1 have exceeded the normal correction range. The ECU can no longer properly compensate for a rich or lean condition by adjusting fuel delivery. This indicates a persistent air-fuel mixture problem that needs investigation.
P0170 is a fuel system-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0170 and illuminates the check engine light.
What are the symptoms of P0170?
If your vehicle has triggered P0170, you may notice one or more of these symptoms:
Check engine light on
Poor fuel economy
Rough or unstable idle
Hesitation or stumbling during acceleration
Possible misfires under load
Failed emissions test
What causes P0170?
Here are the most common causes of P0170, ranked by how likely they are to be the culprit:
Generally yes, for short-term driving. You can drive to a workshop but expect reduced fuel economy and possible rough running. If accompanied by misfires or strong exhaust smell, limit driving.
How do you diagnose P0170?
Follow these steps to pinpoint the root cause of P0170:
Use a scan tool to read short-term and long-term fuel trims for bank 1. Values beyond +/- 25% indicate a significant air-fuel ratio problem. Positive trims mean lean, negative trims mean rich
If fuel trims are positive (lean), perform a smoke test or propane enrichment test to find vacuum leaks. Check intake manifold gaskets, PCV hoses, brake booster line, and all vacuum connections
Inspect and clean the MAF sensor with dedicated MAF cleaner spray. A contaminated MAF underreports airflow, causing lean fuel trims
Check fuel pressure with a gauge. Low pressure causes lean trims, high pressure causes rich trims. Compare to manufacturer specifications
Monitor the upstream O2 sensor data. If it is sluggish or stuck, it may be providing incorrect feedback that forces the fuel trims out of range
If trims are negative (rich), check for leaking injectors by performing a fuel injector balance test or checking for fuel smell in the oil
How much does P0170 cost to fix?
Repair costs for P0170 vary depending on the root cause and your vehicle. Here are typical estimates:
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Clean MAF sensor
€5–€15
€15–€40
€20–€55
Easy
Fix vacuum leak (hose replacement or manifold gasket)
€10–€80
€40–€200
€50–€280
Moderate
Replace MAF sensor
€40–€200
€20–€50
€60–€250
Easy
Replace O2 sensor (bank 1, sensor 1)
€30–€150
€40–€120
€70–€270
Moderate
Fuel injector cleaning or replacement
€30–€300
€60–€200
€90–€500
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0170 on specific vehicles
P0170 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:
P0170 on Mercedes C-Class
Mercedes-Benz C-Class • 2007-2024
The M271 and M274 engines can develop intake manifold swirl flap issues that cause vacuum leaks and trigger P0170. The M274 2.0T is also sensitive to MAF sensor contamination. Mercedes recommends checking the crankcase ventilation system during diagnosis.
What causes P0170 on a Mercedes C-Class?
Mercedes C-ClassIntake manifold swirl flap failure on M271/M274 engines
Estimated costs for Mercedes C-Class ownersadjusted higher than average due to Mercedes-Benz-specific parts pricing
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Clean MAF sensor
€7–€21
€21–€56
€28–€77
Easy
Fix vacuum leak (hose replacement or manifold gasket)
€14–€112
€56–€280
€70–€392
Moderate
Replace MAF sensor
€56–€280
€28–€70
€84–€350
Easy
Replace O2 sensor (bank 1, sensor 1)
€42–€210
€56–€168
€98–€378
Moderate
Fuel injector cleaning or replacement
€42–€420
€84–€280
€126–€700
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0170 on Opel Astra
Opel Astra • 2004-2024
The 1.6L Z16XER and A16XER engines are prone to intake manifold gasket leaks that cause P0170. A common symptom is a whistling noise from the intake area at idle. The PCV system can also contribute to lean fuel trims on higher-mileage engines.
What causes P0170 on a Opel Astra?
Opel AstraIntake manifold gasket leak (whistling at idle)
Opel AstraPCV system valve failure on higher-mileage engines
P0170 repair cost for Opel Astra
Estimated costs for Opel Astra ownersadjusted lower than average due to Opel-specific parts pricing
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Clean MAF sensor
€5–€14
€14–€36
€18–€50
Easy
Fix vacuum leak (hose replacement or manifold gasket)
€9–€72
€36–€180
€45–€252
Moderate
Replace MAF sensor
€36–€180
€18–€45
€54–€225
Easy
Replace O2 sensor (bank 1, sensor 1)
€27–€135
€36–€108
€63–€243
Moderate
Fuel injector cleaning or replacement
€27–€270
€54–€180
€81–€450
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0170 on Ford Focus
Ford Focus • 2005-2024
The 1.6 Ti-VCT and 2.0 GDI petrol engines can trigger P0170 from vacuum leaks at the intake manifold or PCV hoses. The 1.0 EcoBoost is sensitive to MAF sensor contamination from aftermarket air filters. Always use a genuine or high-quality replacement MAF.
What causes P0170 on a Ford Focus?
Ford FocusVacuum leak at intake manifold on 1.6 Ti-VCT
Ford FocusMAF contamination on 1.0 EcoBoost from oiled aftermarket filters
Related diagnostic codes
These codes are often seen alongside P0170 or indicate related issues:
P0170 means the engine computer has detected that its fuel mixture corrections on bank 1 have gone beyond the normal operating range. The system tries to maintain the ideal 14.7:1 air-fuel ratio by adjusting fuel delivery, but something is preventing it from doing so.
What is the difference between P0170 and P0171?
P0170 indicates a general fuel trim malfunction - the trims are out of range in either direction. P0171 specifically means the system is too lean (too much air or too little fuel). P0170 is a broader code that can indicate either lean or rich conditions.
Can a dirty MAF sensor cause P0170?
Yes. A contaminated MAF sensor underreports the amount of air entering the engine, causing the ECU to deliver too little fuel. The O2 sensor detects the resulting lean condition and the fuel trims increase to compensate, eventually triggering P0170.
How do I read fuel trim data?
Use an OBD2 scan tool to view Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT). Values near 0% are ideal. Positive values mean the ECU is adding fuel (lean correction). Negative values mean it is removing fuel (rich correction). Beyond +/- 10% warrants investigation.
Scan your car with Skanyx to diagnose P0170
Connect any Bluetooth OBD2 adapter, scan for codes, and get AI-powered diagnostics with severity ratings and repair cost estimates.
