Fuel and injectionGeneric OBD-II codeUrgency: Garage soon
Code P2188: mixture too rich at idle (bank 1)
P2188 means: too rich at idle (bank 1).[1][2][3] Bank 1 runs with excess fuel only at idle and at low load. The control unit responds by removing fuel through a negative long-term adjustment, and the code is stored when, at idle, that adjustment stays at its rich limit for long enough without the oxygen sensor managing to correct it.[1][2]
What code P2188 means
Bank 1 runs with excess fuel only at idle and at low load. The control unit responds by removing fuel through a negative long-term adjustment, and the code is stored when, at idle, that adjustment stays at its rich limit for long enough without the oxygen sensor managing to correct it.[1][2]
According to AutoDTCs, because the fault is limited to idle, it points to excess fuel or air being measured too low at that speed, rather than to a general engine problem. It is a generic code of the OBD-II standard (it starts with P2), with the same definition on any brand.[1][4]
Original definition (SAE J2012): System Too Rich at Idle Bank 1[1][2][3]
Codes from the same family
They indicate the same problem in a specific cylinder, bank or sensor. Causes, symptoms and diagnosis are those on this page.
Causes of P2188 and its family
From most to least likely, according to the sources.
- 1Fuel pressure too high due to a stuck or faulty regulator.[1][2]
- 2Injector leaking or dripping, which adds unmetered fuel at idle.[1][2]
- 3Dirty, faulty or over-reading mass airflow meter.[1][2]
- 4Upstream lambda sensor contaminated or slow.[1][2]
- 5Evaporative (EVAP) fuel tank purge valve stuck open, which lets fuel vapour into the intake.[1]
- 6Crankcase ventilation (PCV) or vacuum fault.[1][2]
- 7Control unit or software problem, according to CarWiki.[2]
Symptoms
- Irregular idle, hunting or rising and falling, which can end in stalling.[1][2]Engine stalls: faults that cause it
- Black smoke from the exhaust, most visible on starting and at idle.[1][2]Black smoke: faults that cause it
- Smell of unburnt fuel from the exhaust.[1][2]Fuel smell: faults that cause it
- Higher consumption, especially in town.[1][2]Uses more fuel: faults that cause it
- Difficult starting with the engine warm.[1]Hard to start: faults that cause it
- Engine fault warning light on.[1]Engine warning light: faults that cause it
How to diagnose P2188
In order: from the most likely and cheapest to check to the most expensive.
- 1With the engine warm, read the idle fuel trims on the scanner. Confirm that the long-term adjustment is strongly negative at idle and returns to normal on acceleration, and check whether the code is active or only in the history.[1]
- 2Measure the fuel pressure at idle and after switching the engine off. According to AutoDTCs, pressure above the specification points to the regulator; if it falls slowly, to a leaking injector; and if it drops suddenly, to the pump's non-return valve.[1]
- 3Test the purge valve and the injectors: command the valve to close and check whether the negative adjustment reduces; carry out an injector balance test and look for uneven speed drops or dripping.[1]
- 4Inspect the mass airflow meter and the upstream sensor. Compare the idle airflow with the expected figure and look for contamination (silicone, oil, coolant); correct the source before replacing the sensor.[1][2]
- 5Check the crankcase ventilation, whether there is fuel in the oil, the air filter and the vapour tank. After repair, clear the code and check that the long-term adjustment returns to around 0% over a complete driving cycle.[1]
Can I keep driving with P2188?
Garage soon
AutoDTCs rates it as moderate severity: the car can usually be driven, but it is worth repairing soon to protect the catalytic converter, because a sustained rich mixture fouls the spark plugs and eventually loads the catalytic converter with soot.[1]
Parts related to code P2188
The parts that most often cause this code. The code points to the circuit, not always the part: diagnose before you buy.
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Documented faults related to P2188
Known faults of specific engines and cars, with their repair cost, the affected years and their sources.
Injectors: the most serious faults by engine and car
- High severityFrequency: Very frequentOM651Delphi piezo injector failure (220/250 CDI)Yes: 220 and 250 CDI models built between 2008 and 2011 had Delphi piezo injectors that were prone to failing and seizing in the cylinder head. Mercedes-Benz replaced them under warranty in 2009 and switched the 220 CDI to solenoid injectors from 2010-2011, but the 250 CDI kept them.Repair (garage): €3,600–€5,900
- High severityFrequency: CommonBMW N52 / N53N53 piezoelectric injector failureThe N53's piezoelectric direct injectors fail frequently and cause misfires, rough idle and limp mode; replacing them is expensive and they must be coded.
- High severityFrequency: CommonMZR-CDOil dilution from leaking injector seals and DPF regenerationsOn the 2.0 and 2.2 MZR-CD, injector seals that age badly and incomplete particulate filter regenerations on short journeys can let unburnt diesel into the sump, diluting the oil and leaving the engine with less lubrication.
- High severityFrequency: CommonOM642Wear and failure of the Bosch piezo injectorsThe OM642's Bosch piezo injectors can fail from around 150,000-200,000 km, especially with poor-quality diesel; they cannot be repaired, only replaced. Because it is a V engine, those on the rear bank are harder to reach, which pushes up labour costs.Repair: €4,500–€6,500
Mass airflow sensor: the most serious faults by engine and car
- High severityFrequency: Occasional2.0 DTI and 2.2 DTIVP44 injection pump and air mass meter failureGerman Wikipedia documents recurring failures of the Bosch VP44 injection pump and the air mass meter in the early years of this engine. An owner testimony for this engine describes the pump being replaced at 192,500 km, at a cost the owner calls «prohibitive».
- Low severityFrequency: CommonM111Mass air flow sensor failureYes: the M111 mass air flow sensor can fail with use and cause jerking or rough running. English-language Wikipedia documents it on the W210 E-Class, and a French owner survey of the SLK R170 names it as the most-cited fault on that model.
- Low severityFrequency: Common1.8 T 20vAir mass meter (MAF sensor) failureThe air mass meter (MAF sensor) fails fairly often on the 1.8T: on the 150 hp Audi A3 it appears in 3 of the 11 reports collected, and it is also documented on the 180 and 225 hp Audi TT. It causes hesitation and loss of power; it is fixed by replacing the sensor.
- Low severityFrequency: Common1.9 TDIDirty or faulty air flow meter on the 1.9 TDI (loss of power)The air flow meter is a known weak point of the 1.9 TDI: it gets dirty or gives wrong readings, and the control unit limits the engine, causing a sudden loss of power. It is cheap to fix and does not damage the engine.Repair (garage): €100–€300
Lambda sensor: the most serious faults by engine and car
- Medium severityFrequency: Common1.3, 1.5 and 1.6 gasolina (serie M)Faulty catalytic converter and lambda sensors on the 2005-2010 Swift (engine warning light)On the 2005-2010 Swift the catalytic converter often fails at around 50,000 km according to gebrauchtwagenberater.de, and several 1.6 owners cite the lambda sensor. The warning is the engine light; on the Sport the catalytic converter is integrated with the manifold.
- Medium severityFrequency: Occasional1.2 8v FireSensor failures: lambda sensor and crankshaft position sensor (TDC)The 1.2 8v Fire can suffer sensor faults: the lambda sensor (warning light, rough running) and, in the Fiat Punto, the crankshaft position sensor (TDC sensor), linked to misfires. These are minority issues, but they recur across several models with this engine.
- Low severityFrequency: Common1.4 and 1.6 TU3/TU5Sensors that fail: lambda sensor and temperature sensorThe lambda sensor and the coolant temperature sensor are, along with the coils, the components most cited as faulty: they cause an unstable idle, the engine warning light coming on or a cooling fan that does not behave normally.Appears at around 25,000 km
- Low severityFrequency: Common2.0 and 2.4 VVT-iLambda sensor failure on the 1AZ-FE (RAV4 and Avensis 2.0 VVT-i)Lambda sensors are the part that fails most in the RAV4 2.0 VVTi testimonials (about 20 cases among 75 testimonials) and also appear in those for the Avensis 2.0 VVTi; it is a limited-cost fault, not an engine one.Appears at around 150,000 km
Catalytic converter: the most serious faults by engine and car
- Medium severityFrequency: Common1.3, 1.5 and 1.6 gasolina (serie M)Faulty catalytic converter and lambda sensors on the 2005-2010 Swift (engine warning light)On the 2005-2010 Swift the catalytic converter often fails at around 50,000 km according to gebrauchtwagenberater.de, and several 1.6 owners cite the lambda sensor. The warning is the engine light; on the Sport the catalytic converter is integrated with the manifold.
- Critical severityFrequency: Rare1.6 GDI / T-GDIPiston and connecting rod damage from catalytic converter overheating in the naturally aspirated 1.6 GDIIn the US, Kia recalled the 2012-2016 Soul with the naturally aspirated 1.6 GDI: a catalytic converter that overheats can disturb combustion and damage pistons, with a risk of breaking a connecting rod and puncturing the block. We have not found an equivalent warning for this engine in European cars.
- Low severityFrequency: Occasional1.0 VVT-iFaulty lambda sensor (P0420 code) on the 1.0 VVT-iOn the 1.0 VVT-i (1KR-FE) in the Aygo, C1 and 107/108, the lambda sensor, especially the one upstream of the catalytic converter, is documented as failing at high mileage and leaving code P0420 and the engine warning light. It is a cheap repair and does not damage the engine.
- Low severityFrequency: Rare1.6 16v HR16DE / H4MNo documented pattern of chain, catalytic converter or coil failuresUnlike other turbo engines from the same alliance, the sources consulted do not document a pattern of timing chain, catalytic converter or ignition coil failures for this naturally aspirated block: across more than 100 combined accounts, these sections appear empty or, at most, with an isolated case.
- Medium severityFrequency: OccasionalJeep Wrangler JLGearbox wiring harness with insufficient clearance from the catalytic converterTwo British campaigns from 2020 (V78 and W19) asked for the gearbox wiring harness of 664 and 547 Wranglers built between October 2017 and January 2020 to be checked, because it sat too close to the catalytic converter. It is inspected and repositioned, or replaced if the heat has damaged it.
P2188 by make
Documented faults that can trigger P2188 in each make's engines and cars.
Frequently asked questions
Why does it only appear with the engine at idle?
According to AutoDTCs, because the fault is limited to idle it points to excess fuel or air being measured too low at that speed, rather than to a general engine fault. That is why the fuel pressure, the injectors, the mass airflow meter and the purge valve are checked first.[1]
Can I keep driving with P2188?
AutoDTCs rates it as moderate severity: the car can usually be driven, but it should be repaired soon, because the excess fuel fouls the spark plugs and loads the catalytic converter with soot.[1]
How does it differ from P2187?
They are the same idle case in opposite directions: P2187 is a mixture that is too lean and P2188 one that is too rich. That is why the causes change: here the pressure regulator, leaking injectors and the purge valve are checked first.[1][2]
And if the code is P2190?
It is the same problem on bank 2: mixture too rich at idle. It is diagnosed in the same way, by measuring the fuel pressure and that bank's trims.[5][6]
Will I pass the MOT with code P2188?
If the code has switched on the engine warning light, no: with that light on, the inspection records a serious defect, and on Euro 5 and Euro 6 cars the ITV (Spain's roadworthiness inspection, similar to the MOT) also reads the OBD diagnostic system. Repair the fault before you go; clearing the code just before the inspection does not help either, because it counts as a serious defect.[7]
Not sure what is wrong with your car? Describe what you notice in the symptom diagnosis or see all fault codes.
Sources
Every fact on this page links to its source. If you find an error, let us know.
- P2188 – System Too Rich at Idle Bank 1 — AutoDTCsAutoDTCs · Technical documentation · published August 2026 · consulted 31 October 2026
- OBD DTC Fehlercode P2188 | System im Leerlauf zu fett, Bank 1CarWiki.de · Technical documentation · consulted 31 October 2026 · in German
- p2188 Generic DTC: System Too Rich at IdleDTCSearch.com (OBD Solutions) · Technical documentation · consulted 31 October 2026
- On-board diagnosticsWikipedia · Other source · consulted 31 October 2026
- P2190 – System Too Rich at Idle Bank 2 — AutoDTCsAutoDTCs · Technical documentation · consulted 31 October 2026
- p2190 Generic DTC: System Too Rich at IdleDTCSearch.com (OBD Solutions) · Technical documentation · consulted 31 October 2026
- Desmontando mitos: ¿puede pasar mi coche la ITV con el testigo de «avería motor» encendido?Diariomotor · Motoring press · published 8 March 2021 · consulted 2 October 2026 · in Spanish