Rav4.2 B2798 Communication Malfunction No. 2 During Learning.

[Joylove]

Hi I am learning a used transponder to a 2001 UK RAV4 to create a spare key (#2 Master).

I have Master key #1.

All other transponders have been deleted.

Master key 1 starts the car fine.

During the part of the learning where the new key is being accessed (duration 80s) this fault appears at about 50 seconds.

I have tried 4 times to add this key, clearing the DTC code first each time, DTC appears at the same time.

Any ideas?

Thanks

[shcm]

I'm not familiar with the Toyota system, but do you have an unused transponder?

Following is all pure guess work on my part, but I know on some transponders there are memory bank areas (EEPROM) which can have a write protect bit set on them.

Possibly the car expects a blank transponder (apart from the unique ID some have) where everything is writeable and it sets protection bits once the programming is complete. Possibly the system may not have the capability to clear the write protect bit(s) that have been set?

That would possibly give rise to a write or comms error, when the thing was trying to verify what it thought it had written.

Are there markings on the transponder pill? Can you find a data sheet. It might give a few more clues.

[Joylove]

That was my main worry. I'll have to pull the remote apart to find the chip, and hope it's not fixed down permanently.

I just thought others had done this mod (aftermarket spare key) a thousand times.

[shcm]

I just thought others had done this mod (aftermarket spare key) a thousand times.

Yes, but wouldn't you expect them to start with an unused and therefore possibly previously un-programmed key?

[Joylove]

Yes, but wouldn't you expect them to start with an unused and therefore possibly previously un-programmed key?

Not by looking at the rampant bidding that goes on on eBay. Every used Toyota key goes for £20-30; even when started at £0.01.

Anyway, pulled mine apart today, it's not marked but looks like a PCF7930/PCF7935; which are backwards compatible with each other and do indeed have a write protect bit. I have a Gambit RFID programmer for those and it never occurred to me to check if it was set.

One for the back burner, I damn near destroyed the fob taking it apart because it was glued and brittle.

[Joylove]

So I had a bit of a play. I tried learning a couple of PCF7930AS to the car, no joy, communication errors with these chips reported in the ECU fault log.

Also tried reading the Toyota chips with a Gambit II, also not possible, so the chip is not a PCF793x or EML, Temic or Megamos compatible device.

It strikes me that the chip in the key is likely not needing to be written to by the ECU, rather that the ECU accepts the chip code. I say this because the existing chips coded to the the car can be deleted and reassigned a position. That is, chip 4 Master became chip 1 Master when I deleted all old keys. There is no maximum number of times this can be done.

Suggested to me that, unlike say the Bosch implementation, there are not 10 valid chip codes allowed and the blank chip must be written to meet one of those codes in the factory. Once 10 chips are used up, it's game over, new ECU coding required. Once in use these codes will roll.

Just hypothesising.

I'll have another hunt on Google to see if the Toyota Chip type is known and available to purchase.

[Joylove]

Just to wrap this up, after a few wasted purchases of the wrong key (DENSO, Valeo corolla), loose blank ID4 chips and more, it became obvious from the different part numbers for the master key guts that I had to have a RAV4 factory coded key.

So I found one and it coded to the immobiliser first time.

So you need to check if your replacement remote guts are DENSO* or VALEO* and that it's from the same model vehicle.

*Valeo keys have black or gold toyota badges, have Valeo stamped on the key blade and recessed UNLOCK and LOCK text.

*DENSO keys the centre groove on the key blade goes almost all the way to the fob. The LOCK/UNLOCK text on the case is embossed. The Badge is gold. The nipple on the lock button is a different size.