Symptom
Stop-start system not working
The engine no longer switches itself off at a standstill. Frequently not a fault in the stop-start system at all — it withdraws itself whenever any of its many preconditions is unmet, and it does so silently. A clutch or brake switch it cannot trust, a battery below its state-of-charge threshold, a cabin still far from the requested temperature, or an engine not yet warm will each suppress it entirely. So this is a symptom that usually points somewhere else, and the most common somewhere else is a cheap switch rather than anything expensive.
Also described as: stop start not working, auto stop not working, engine doesn't stop at lights, start stop disabled, idle stop not working, eco stop not working, سیستم توقف و حرکت کار نمیکند, استارت استاپ کار نمیکند, sistema start stop no funciona, auto stop no funciona, start stop no activa, نظام التوقف والتشغيل لا يعمل, ستوب اند ستارت معطل, خاصية إطفاء المحرك لا تشتغل
What this usually means
Most of the time nothing is broken. Stop-start withdraws itself whenever any one of a long list of preconditions is unmet, and it does so silently — there is no lamp for "I have decided not to". So the honest first question is not what has failed but which condition the car is refusing on, and a scan tool that can read the inhibit reason answers in seconds what guesswork does not answer at all.
Battery state of charge is the commonest single reason, and it is measured rather than assumed. An intelligent battery sensor reports charge, current and temperature to the body module, and the function is disabled the moment the estimate falls outside its window. Two consequences follow that surprise people. A battery replaced without being registered leaves the management working from the old battery's profile, so the estimate stays wrong and stop-start never returns however good the new battery is — a fault that presents as "it stopped working after I changed the battery" and is a configuration job rather than a repair. And because the estimate is charge, not health, a car doing only short journeys can lose the function seasonally while nothing has failed at all.
The rest of the list is cheap switches and ordinary conditions: a brake or clutch switch the module cannot trust, a bonnet switch reading open, a seatbelt or door signal, an engine not yet at temperature, a cabin far from the requested temperature with the climate system demanding the compressor, a steep gradient, a tight steering angle, or a very cold or very hot ambient. Each of these is the system working correctly.
So the reason to investigate is a pattern, not an instance. Never stopping in cold weather is expected. Never stopping at all, in any conditions, for months, is worth reading the inhibit reason for — and the answer is usually a switch costing very little.
Working through it
| What you find | Likely cause | How to confirm it | What fixes it |
|---|---|---|---|
| Stopped working immediately after a battery change and never came back | The replacement was not registered, so energy management still works from the old battery's profile and never reaches the required state of charge | Read the battery data stored in the energy-management module and compare it with the battery actually fitted. Check the reported state of charge against a measured one. | Register the battery — type, capacity and serial — with the manufacturer's tool or an equivalent. Check the type matches too: AGM replaced with flooded is its own fault. |
| Works in mild weather, never in cold, returns in spring | Nothing — state of charge and battery temperature both sit outside the permitted window in cold conditions | Read the inhibit reason and the battery sensor's reported temperature and charge. Confirm the pattern is seasonal before doing anything. | No repair. A longer journey or a maintenance charge restores it; a car used only for short trips will lose it again. |
| Never stops, in any conditions, with no warning lamp | A precondition permanently unmet — most often a brake or clutch switch the module will not trust | Read the inhibit reason on a scan tool, then watch the brake and clutch switch live values against the pedals being pressed. A switch reading pressed at rest is the answer. | Renew the failed switch and adjust it properly. These are among the cheapest parts on the car. |
| Stopped working after bonnet, wing or front-end work | Bonnet switch reading open — the system will not stop the engine if it believes the bonnet is raised | Check the bonnet switch live state against the bonnet's real position, and inspect the switch and its striker for damage or misalignment. | Realign or renew the switch. Check the alarm's bonnet input at the same time; it is usually the same switch. |
| Stops only sometimes, with the climate control working hard | Cabin temperature far from the requested one, so the system holds the engine on to keep the compressor turning | Reproduce with the climate system off or in a settled cabin. The behaviour changing with climate demand confirms it. | No repair. If the cabin never settles, diagnose the climate fault on its own findings. |
| Engine stops but restarts immediately, repeatedly | A demand appearing after the stop — falling charge, brake vacuum, or climate — so the system reverses its own decision | Watch state of charge and brake servo vacuum across the stop event. A charge that dives the moment the engine stops is a battery that cannot hold the load. | Test and renew the battery on a conductance test, and register it. Investigate vacuum supply where that is the trigger. |
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Stopped working immediately after a battery change and never came back
- Likely cause
- The replacement was not registered, so energy management still works from the old battery's profile and never reaches the required state of charge
- How to confirm it
- Read the battery data stored in the energy-management module and compare it with the battery actually fitted. Check the reported state of charge against a measured one.
- What fixes it
- Register the battery — type, capacity and serial — with the manufacturer's tool or an equivalent. Check the type matches too: AGM replaced with flooded is its own fault.
-
Works in mild weather, never in cold, returns in spring
- Likely cause
- Nothing — state of charge and battery temperature both sit outside the permitted window in cold conditions
- How to confirm it
- Read the inhibit reason and the battery sensor's reported temperature and charge. Confirm the pattern is seasonal before doing anything.
- What fixes it
- No repair. A longer journey or a maintenance charge restores it; a car used only for short trips will lose it again.
-
Never stops, in any conditions, with no warning lamp
- Likely cause
- A precondition permanently unmet — most often a brake or clutch switch the module will not trust
- How to confirm it
- Read the inhibit reason on a scan tool, then watch the brake and clutch switch live values against the pedals being pressed. A switch reading pressed at rest is the answer.
- What fixes it
- Renew the failed switch and adjust it properly. These are among the cheapest parts on the car.
-
Stopped working after bonnet, wing or front-end work
- Likely cause
- Bonnet switch reading open — the system will not stop the engine if it believes the bonnet is raised
- How to confirm it
- Check the bonnet switch live state against the bonnet's real position, and inspect the switch and its striker for damage or misalignment.
- What fixes it
- Realign or renew the switch. Check the alarm's bonnet input at the same time; it is usually the same switch.
-
Stops only sometimes, with the climate control working hard
- Likely cause
- Cabin temperature far from the requested one, so the system holds the engine on to keep the compressor turning
- How to confirm it
- Reproduce with the climate system off or in a settled cabin. The behaviour changing with climate demand confirms it.
- What fixes it
- No repair. If the cabin never settles, diagnose the climate fault on its own findings.
-
Engine stops but restarts immediately, repeatedly
- Likely cause
- A demand appearing after the stop — falling charge, brake vacuum, or climate — so the system reverses its own decision
- How to confirm it
- Watch state of charge and brake servo vacuum across the stop event. A charge that dives the moment the engine stops is a battery that cannot hold the load.
- What fixes it
- Test and renew the battery on a conductance test, and register it. Investigate vacuum supply where that is the trigger.
Codes that produce this symptom (65)
Listed with the codes that most typically present this way first — the likeliest place to start.
- P00FD Battery B State of Charge Performance Typical of this code Moderate
- P058C Battery Monitor Module Temperature Monitoring Performance Typical of this code Moderate
- P05BD Stop-Start Mode Switch Circuit Range/Performance Typical of this code Low
- P061E Internal Control Module Brake Signal Performance Typical of this code High
- P06E9 Engine Starter Performance Typical of this code Moderate
- P06EF Engine Restart Performance Typical of this code Moderate
- P0830 Clutch Pedal Switch A Circuit Typical of this code Moderate
- P0831 Clutch Pedal Switch A Circuit Low Typical of this code Moderate
- P0832 Clutch Pedal Switch A Circuit High Typical of this code Moderate
- P0833 Clutch Pedal Switch B Circuit Typical of this code Moderate
- P0834 Clutch Pedal Switch B Circuit Low Typical of this code Moderate
- P0835 Clutch Pedal Switch B Circuit High Typical of this code Moderate
- P0A1E Starter/Generator Control Module Typical of this code Moderate
- P0B00 Electric/Auxiliary Transmission Fluid Pump Motor Phase U Current Typical of this code High
- P0B01 Electric/Auxiliary Transmission Fluid Pump Motor Phase U Current Low Typical of this code Moderate
- P0B02 Electric/Auxiliary Transmission Fluid Pump Motor Phase U Current High Typical of this code Moderate
- P0B03 Electric/Auxiliary Transmission Fluid Pump Motor Phase V Current Typical of this code High
- P0B04 Electric/Auxiliary Transmission Fluid Pump Motor Phase V Current Low Typical of this code Moderate
- P0B05 Electric/Auxiliary Transmission Fluid Pump Motor Phase V Current High Typical of this code Moderate
- P0B06 Electric/Auxiliary Transmission Fluid Pump Motor Phase W Current Typical of this code High
- P0B07 Electric/Auxiliary Transmission Fluid Pump Motor Phase W Current Low Typical of this code Moderate
- P0B08 Electric/Auxiliary Transmission Fluid Pump Motor Phase W Current High Typical of this code Moderate
- P0B09 Electric/Auxiliary Transmission Fluid Pump A Motor Supply Voltage Circuit/Open Typical of this code High
- P0B0A Electric/Auxiliary Transmission Fluid Pump A Motor Supply Voltage Circuit Low Typical of this code Moderate
- P0B0C Electric/Auxiliary Transmission Fluid Pump A Hydraulic Leakage Typical of this code High
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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