F430 Red Slow Down Light / Thermocouple Replacement

Although the car hasn’t been getting driven much due to weather, I had encountered a issue with getting the dreaded RED slow down light on the dash shortly after startup. This indicates that the catalytic converters are are over heating and various protection will be applied, up to and including shutting down the offending bank of cylinders.

I concluded it likely was a spurious warning as it happens right after cold start, and using a IR thermometer to confirm, both catalytic converters were no where near where it should start alarming. Note, if the slow down light is not . Also a AMBER colored slow down light indicates a issue with the e-diff and nothing to do with the cat temperatures.

Pulling codes from both the right and left ECU confirmed that something was up with the right engines measurements. P0428 indicates that we have elevated temperature. P1446 indicates that corrective action of shutting down the bank had occured.

Interestingly, the left bank was also showing multiple misfires from the shutdown. I attribute this being on the left bank only due to the detection strategy the Motronic ECUs employ.

This is also a common problem on older Ferrari’s as well (namely the 360 and things prior). In those cases, not only do they have a thermocouple that may go bad, but a small voltage amplifier (also known as a Cat ‘ECU’) that tend to go south. In the case of the F430, the thermocouple amplifier is located in the ECU itself and so there isn’t a separate for this. Of additional note, Ferrari moved to a software based estimation model that did completely away with the thermocouples in 2007 and later models and instead have a small plug in the bung that the thermocouple normally attaches to. This gets rid of a obvious failure point.

Replacement of the thermocouple if fairly straight forward.

Step 1 involves removing the two side panels of the offending side. Its a matter of unscrewing several 3mm hex bolts all around the perimeter. Additionally, you’ll need to detach the gas strut on the lid. To do so, use a small screwdriver to pop off the metal retaining clip on the joint.

I recommend possibly replacing the screws with something that isn’t made of the soft aluminum. I found these were very easy to strip and ran into problems with ones that the previous person to mess with the car had stripped. I wasted a lot of time getting this part off.

With the panels out of the way, its fairly easy to now see and access the thermocouple.

The thermocouple is circled in red. Simply use a 17mm wrench to unscrew it.

Next, try and follow the wiring harness back up to the top where it terminates at the connector. You may need to cut any zipties that are holding it on.

Trying to trace this, I thing I found a potential reason why this sensor failed. Whoever last routed the cable actually routed it in such a way that the inner wheel well was sandwiching the cable between it and the frame! It was internally broken at this pinch point. I ended up having to loosen the wheel well in order to get the cable out. The green line below shows the path the thermocouple cable took and the poor re-assembly that happened.

Now, that the thermocouple is freed, remove the 10mm bolt holding it to the frame. The O2 sensor connector is attached to the same bolt. The trick to releasing the connector is to use a small screwdriver coming in from the side of the thermocouple itself to gently lift up the latch.

And here is the full sensor.

The part number is 200934. I ended up going with a aftermarket version from Superformance which was about $115USD (plus all shipping, duties, etc). The Ferrari branded version is about $185USD.

Before discarding the old sensor, remove the metal bracket. It simply pulls out (but is a bit difficult). Likewise, recover the cable clamp (if yours has one — mine was missing it) as well and transfer both to the new sensor.

Simply reinstall the sensor. It included a small tube of copper antiseize that I put on the thread of the header before tightening it down. Then, using zip ties nicely route the cable back up and install the 10mm bolt holding the bracket together. Button it all up and you’re done.

From there, clear the codes and fire the car back up and monitor to see if the fault returns. I happily can say that they seem to be now gone in my case.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

Blog at WordPress.com.

Up ↑

%d bloggers like this: