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BMW fault code 118001: fuel-air mixture too lean / too rich
Mixture control fault. What the code means, its most common causes and what to do.
Codes in this family
Six-digit BMW codes stored by the engine control unit (DME). The same code appears in this form in ISTA and in the MOSTUNED app.
| Code | Meaning |
|---|---|
| 118001 | Mixture control: Fuel-air mixture too lean |
| 118002 | Mixture control: Fuel-air mixture too rich |
| 118401 | Mixture control: Mixture too lean, deviation too high |
| 118402 | Mixture control: Mixture too rich, deviation too high |
What does 118001 mean?
The DME constantly trims fuelling using the oxygen (lambda) sensor. When that trim hits its limit, meaning the engine has to add or remove far more fuel than normal to hold the requested mixture, these codes are stored. Lean means too much air for the fuel; rich means too much fuel for the air.
Most common causes
Top to bottom, starting with what is easiest to check.
| Cause | What to check |
|---|---|
| Unmetered air (vacuum leak) | Intake manifold seals, the crankcase ventilation line and the valve-cover membrane are the most common causes of a lean mixture. |
| Fuel pressure | If the low-pressure pump, filter or high-pressure pump cannot supply enough fuel, the mixture goes lean. |
| Injector | A restricted injector gives a lean mixture; a leaking one gives a rich mixture. |
| Tank vent valve | A valve stuck open feeds uncontrolled fuel vapour into the mixture. |
| Oxygen sensor | An aged sensor reads wrong and the DME trims in the wrong direction. |
Can you drive with this code?
The car mostly drives normally, though idle may hunt. Running lean under high load is hard on the engine, so have the cause found before using full throttle.
How it relates to tuning
On a healthy car a properly prepared calibration does not create mixture faults. Our calibrations keep fuel-trim limits and lambda monitoring in place; if this code appears after tuning it is almost always an existing leak or fuel-supply weakness showing up at high load. The lambda and fuel-trim channels in the Logger narrow down the cause.
Read the code yourself, free
- 1 Install MOSTUNED on your iPhone.
- 2 Connect to the car with an ENET cable or WiFi-ENET adapter.
- 3 Open “Fault Codes” under Diagnostics; stored codes are listed with their descriptions.
- 4 Note the code, fix the cause, then clear it from the same screen and read again to confirm.
Frequently asked questions
What does BMW fault code 118001 mean?
The DME constantly trims fuelling using the oxygen (lambda) sensor. When that trim hits its limit, meaning the engine has to add or remove far more fuel than normal to hold the requested mixture, these codes are stored. Lean means too much air for the fuel; rich means too much fuel for the air.
Can I drive with code 118001?
The car mostly drives normally, though idle may hunt. Running lean under high load is hard on the engine, so have the cause found before using full throttle.
Does clearing 118001 fix the problem?
Clearing removes the entry, not the cause. If the cause remains, the code returns when the conditions occur again. The right order is: read the code, fix the cause, clear it and read again to confirm.
How do I read code 118001?
You read it for free with the MOSTUNED app: connect your iPhone to the car with an ENET cable or WiFi-ENET adapter and open Fault Codes under Diagnostics. Bluetooth OBD (ELM327) adapters do not provide this connection.
Does tuning cause this code?
On a healthy car a properly prepared calibration does not create mixture faults. Our calibrations keep fuel-trim limits and lambda monitoring in place; if this code appears after tuning it is almost always an existing leak or fuel-supply weakness showing up at high load. The lambda and fuel-trim channels in the Logger narrow down the cause.
I cannot find the cause. What should I do?
Send us your car model, the code and a Logger recording if you have one on WhatsApp and we will look at it together. Related codes: 118002, 118401, 118402.
Next step
- All BMW fault codes — B48 / G-series code guide
- Download the app — Fault reading and clearing are free
- ENET cable and adapter guide — What you need to connect
- Using the Logger — Narrow down the cause with live data
Contact
Not sure?
Send your model, hardware and goal — we will pick the right package together. We do not sell what does not fit.