Cold Start Off — disabling the catalyst heating mode

Cold Start Off disables the catalyst heating mode that runs after a cold start, in the ECU software of a petrol engine. The engine no longer holds a raised idle and retarded ignition when cold, so start-up becomes quieter and smoother. For tuners: send us the original file and get a ready-to-flash file with corrected checksums, on average in 30–60 minutes.

Why a cold engine roars and idles high

After a night outside the catalyst is cold, and it only cleans the exhaust efficiently from about 300–350 °C. According to Hella, up to 80% of the emissions of a whole drive cycle are produced during the cold start. So for the first few tens of seconds the manufacturer uses the engine itself to heat the catalyst.

The ECU does two things. It raises the idle speed: a 1997 Siemens patent gives 1,100–1,400 rpm, against the usual 600–1,000 rpm of a passenger car. And it retards the ignition hard: the mixture burns later, already on the expansion stroke, so there is less torque and more heat in the exhaust. Bosch states in its patent that catalyst heating depends heavily on late ignition timing.

That is the familiar cold-start sound: a high, steady drone and slightly rough running. With a sports exhaust or no catalyst it gets properly loud. On BMWs, according to the developers of the MHD platform, the mode lasts about 45 seconds. Other makes have their own timing, usually around a minute. On some engines the secondary air pump runs at the same time, and that is disabled by a separate option, SAP Off.

Who actually needs it

What changes in the software

The option removes the catalyst heating mode and nothing else. The rest of the cold-start logic stays as the factory set it.

The monitoring deserves a word of its own. From the 2009 model year, California's OBD II rules (CARB) require the ECU to check the raised idle and the ignition retard during warm-up. If they do not respond to the command, the Check Engine light comes on: that is where P050A (cold start idle air control system performance) and P050B (cold start ignition timing performance) come from. So the file disables both the mode and its check, where the software has one.

The rest of the calibration is unchanged and checksums are recalculated. Other options can go in the same order, for example Stage 1.

What the car gives up without catalyst heating

The catalyst reaches its working temperature later, and until then the exhaust is barely cleaned. CO and unburnt hydrocarbon emissions in the first minutes after a start go up, which is exactly why the manufacturer runs this mode. There is no other noticeable difference: only the first seconds after a cold start become quieter and smoother, and a warm engine drives exactly as before.

What to do before and after flashing

• If the engine misfires or starts badly when cold, find the cause first: Cold Start Off does not cure that.
• If the engine has a secondary air pump that whines or sets faults, add SAP Off to the order.
• After flashing, let the car cool down for a few hours and do a cold start: the idle should drop quickly after the start, with no long drone and no faults.

How to order the file

1. Read the original file via OBD or on the bench with the tool you use. We need an unmodified stock file.
2. Upload it to the portal and select COLD START OFF. Other options can go in the same order.
3. Get the finished file with recalculated checksums, on average within 30–60 minutes.
4. Flash the file, clear the faults and check a cold start.

Supported ECUs are listed below. If yours is not there, send the file with a request and we will check whether there is a solution for that software.

Without catalyst heating, CO and hydrocarbon emissions rise after a cold start and the vehicle no longer matches its emissions class. In the EU, the UK, the US and a number of other countries tampering with emission control is prohibited on public roads and may cause an inspection failure. The service is intended for tuners and is used where the law allows it: motorsport, off-road, export, vehicles not used on public roads. Responsibility for using the file lies with the vehicle owner.