General: Start Prevented Try Again - Key Too Warm!

[XC90Seaborne]

We've been having the "start prevented try again" message come and go on our 2011 XC90

It started off as only happening to me and not my wife and considering it's her daily car it seemed strange and thought the car simply doesn't like me or there's some weird way I'm putting the key in the ignition.

It wouldn't happen to me when leaving home it was always on the return journey.

Long story short we figured out when out with the car I kept the key in my trouser pocket my wife kept it in her handbag. My body heat warmed the key but in the handbag, it didn't get warm.

So whenever I had the problem I just left the key to cool and in 2-3 minutes it worked. As a preventative, I used coat pockets not trouser pockets, etc I wasn't going to go down the route of a handbag for me just yet.

This happens with both keys and now with the warm weather simply leaving the key in the car on a warm day has this effect as experienced by my wife yesterday... Warmer days are harder to cool the key down

Question is. Why? Has anyone else noticed this? I thought the transponder part of the key is passive as in not requiring battery power like an RFID and I can unlock from a good distance which makes me think the battery is good in both keys

Any ideas / Help?
Yes, I had to put the key in the fridge at work the other day to get home. this cant continue!

Cheers Seaborne

[Tannaton]

Originally Posted by XC90Seaborne

We've been having the "start prevented try again" message come and go on our 2011 XC90

It started off as only happening to me and not my wife and considering it's her daily car it seemed strange and thought the car simply doesn't like me or there's some weird way I'm putting the key in the ignition.

It wouldn't happen to me when leaving home it was always on the return journey.

Long story short we figured out when out with the car I kept the key in my trouser pocket my wife kept it in her handbag. My body heat warmed the key but in the handbag, it didn't get warm.

So whenever I had the problem I just left the key to cool and in 2-3 minutes it worked. As a preventative, I used coat pockets not trouser pockets, etc I wasn't going to go down the route of a handbag for me just yet.

This happens with both keys and now with the warm weather simply leaving the key in the car on a warm day has this effect as experienced by my wife yesterday... Warmer days are harder to cool the key down

Question is. Why? Has anyone else noticed this? I thought the transponder part of the key is passive as in not requiring battery power like an RFID and I can unlock from a good distance which makes me think the battery is good in both keys

Any ideas / Help?
Yes, I had to put the key in the fridge at work the other day to get home. this cant continue!

Cheers Seaborne

You're correct the transponder that is read when the car is started is similar to a passive RFID in that it is powered by a magentic field from a coil around the ignition barrel rather than a battery. The coil and reader are a single unit and sometimes give intermittent problems but how that translates to keys not working when they are warm I have no idea......

Unfortunately this is a situation that can be difficult to diagnose, if I recall correctly the reader is circa £100 but getting a new key is circa £300 and the latter can only be done by dealers. I worked on a car with similar issues a few years back (not temp related) and eventually found a dealer who would spend some time diagnosing it, and they couldn't pin point the cause. The customer then agreed to have the reader and both keys replaced at a cost of over £800 but this did sort it.

[SwissXC90]

As Tannaton says, very dificult to diagnose

I'm a trained and qualified radio engineer.

The ring antenna around the ignition lock sends out a signal to the key, and activates the passive transponder in the key.

The key transponder takes the radio signal, uses a sniff of it for power, and sends back a unique serial number.

The ring antenna receives the (very weak) signal, and decodes the key's serial number, and passes it down the line to the engine control unit.

So the big question is: Why does the key behave differently when warm? And why do both keys have the same symptoms?

It is statistically highly unlikely that 2 x keys have identical problems at the same time, so thus logic says it is more likely the ring antenna at fault.

The ring antenna may be struggling with detecting the signal, and the warm key may be sending back slightly less signal, or a slightly different frequency.


Thus I would recommend the following actions:

1. New ring antenna. Observe behavior for a few weeks. If symptoms persist, then:

2. 2 x new keys

Note that changing the battery in the keys makes no difference.
The battery is only for the remote lock/unlock, and plays no part in the immobilizer.

PS: I've also seen the same message as you, but only about two times in the last 4 years. So no concern for me.