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2001 Ford Focus 1.6 UK - P0172 Fault Code: Rich Running, MAF & Lambda Sensor Diagnosis

Model: 2001 Ford Focus 1.6 Fault Code: P0172 Posted: 2008-11-22 19:00

Hi everyone, I'm based in the UK and driving a 2001 Ford Focus with a 1.6L engine. This forum is US-focused, but I hope this information still helps. I recently picked up an OBDII code P017-2 using Digimoto Lite, which appears when the engine warning light is on. The reading was taken at idle/tickover after a 20-mile drive — the engine was fully warmed up. The AA (recovery service) previously visited and advised that my engine is running rich on Bank 1. They mentioned that Lambda Sensor 2 on Bank 1 wasn't sending data, suggesting it should be cleaned or replaced. I haven’t yet done this. After rechecking with my own OBDII reader, I now see that Lambda Sensor 2 on Bank 1 is reporting data — but Lambda Sensor 2 on Bank 2 shows no signal. My question: do standard 4-cylinder engines like the 2001 Ford Focus have a 'Bank 2'? If so, where is this sensor located? I’ve also noticed that I re-oiled my K&N air filter last night — I read online that oil-based filters can interfere with the Mass Airflow (MAF) sensor and cause the engine to run rich. Could this be why the warning light came back on? Lastly, could anyone confirm whether the other data in the OBDII reading is within normal range? For example: MAF readings, fuel trim values, ignition timing, or fuel pressure? Thanks for any insights — I'm trying to diagnose this without a full workshop visit.

Related fault codes

P0172

Comments (2)

Anonymous 2008-11-24 09:32

Check and clean the MAF sensor as well as inspect wiring connections. Replace your K&N filter with a standard paper filter. Also verify for vacuum leaks or exhaust system issues. Note that Bank 2 is not relevant in most 4-cylinder engines — this may be a misinterpretation of the OBDII data. Good luck and please update if you find any resolution.

Anonymous 2008-11-28 18:14

I'm not certain about the exact fuel system configuration in UK-spec 2001 Ford Focus models — there may be differences between North American and European versions. Your fuel trim readings indicate a significant rich condition at idle. The absence of MAF data suggests the engine is running on fuel tables or using a MAP sensor instead (though I'm unsure if 4.5 PSI is within acceptable range). Ignition timing appears advanced — is it actually 64° or 6.4°? I strongly recommend fixing the MAF issue, as it may stem from an electrical connection fault, broken hot wire, or contamination. Check fuel pressure at the fuel rail — elevated pressure could point to a faulty fuel pressure regulator or a blockage in the return line (if your system uses one). Also ensure vacuum hoses are intact and functioning properly. Fuel pressure should be lower at idle than under open throttle. Another possibility: leaking or sticking injectors. Does the car struggle to start when hot? I’d also recommend removing the K&N filter for inspection — while performance filters can work well in modified cars, they often cause MAF contamination and poor air filtration in stock vehicles. A potential issue could be a purge valve leak in the evaporative emissions system. Induction vacuum might draw fuel vapors directly from the carbon canister when the purge solenoid should be closed — though this typically triggers a specific code. O2 sensor sticking rich is another possibility. Did you observe Lambda Sensor Bank 1, Sensor 1 voltage fluctuating between 0.1 and 0.9 volts? A stable 14.6:1 fuel ratio requires constant switching between rich and lean — if this doesn’t occur, the P0172 code may not appear. This behavior only happens when the engine is at normal operating temperature. In a standard inline-4 engine like the 2001 Ford Focus, there's typically only one bank of injectors. Therefore, Lambda Sensor 2 on Bank 1 is actually a catalyst sensor — it monitors converter performance and does not affect air-fuel ratio. This helps clarify why Bank 2 may be irrelevant. Best of luck with your diagnosis!