Engine related wiring problems involving turbo control?

[Peter Monaghan]

Hi all im new to this site and wonder if anybody can help, i keep getting a P1251 code along with limp mode, are there any known engine wiring loom faults ?

ps sorry for posting in wrong place to begin with 🤪 tia.

[Peter Monaghan]

I take it no one has any ideas as quite a few people have read post!

[RAV4-D4D]

Hi Peter - I haven't experienced the P1251 code but based on a few posts about P1251 people seem to suggest it may be a sign of turbo failure, perhaps you can expand on why you're thinking it may be wiring loom related?

 

 

[Peter Monaghan]

Hi John the description for the DTC is, step motor for turbocharger control circuit ( intermittent ), it only used to happen under full load but is now holding back at half throttle, have replaced fuel and air filter and cleaned air flow meter.

[Devon Aygo]

17 hours ago, Peter Monaghan said:

Hi John the description for the DTC is, step motor for turbocharger control circuit ( intermittent ), it only used to happen under full load but is now holding back at half throttle, have replaced fuel and air filter and cleaned air flow meter.

P1252 is step motor for turbocharger control circuit ( intermittent )

P1251 is an Overboost condition is usually caused by either stuck/sticking stepper motor or stuck/sticking VNT( Variable nozzle turbo )

[Peter Monaghan]

Have put a turbo boost gauge on it and it never goes above 20 psi its mostly 10-15 psi!

[Devon Aygo]

2 hours ago, Peter Monaghan said:

Have put a turbo boost gauge on it and it never goes above 20 psi its mostly 10-15 psi!

The diag process is more centred on vacuum & electrical function than Turbo pressures, I suggest you spend a few £, register and login to www.toyota-tech.eu go to repair manual, diagnosis and select P0234 ( includes P1252 & P1251 diag ) and follow the step by step diagnostic 

[RAV4-D4D]

If you're reading boost from the OBD then 10-15 is about right. I rarely see 15 (never higher) and I have to accelerate very hard for that.

[Peter Monaghan]

Running problems sorted, no more P1251 codes or turbo replacement!

[Peter Monaghan]

On 4/2/2022 at 12:00 AM, Peter Monaghan said:

Hi John the description for the DTC is, step motor for turbocharger control circuit ( intermittent ), it only used to happen under full load but is now holding back at half throttle, have replaced fuel and air filter and cleaned air flow meter.

 

On 4/27/2022 at 6:43 AM, RAV4-D4D said:

If you're reading boost from the OBD then 10-15 is about right. I rarely see 15 (never higher) and I have to accelerate very hard for that.

Gave it a 380 mile run up to Nuneaton and back at between 60-75 mph, it now runs sweet as a nut, obviously very sooted up and fuel consumption has gone from 32 mpg back up to over 45 mpg round town.

[Cyker]

Thanks for coming back and letting us know how you got on!

Must admit I wouldn't have guessed that giving it an 'Italian tuneup' (aka thrashing the nuts off it  ) would fix such issues but there you go! Just goes to show that diesels really do prefer to be used hard!  

[Peter Monaghan]

6 minutes ago, Cyker said:

Thanks for coming back and letting us know how you got on!

Must admit I wouldn't have guessed that giving it an 'Italian tuneup' (aka thrashing the nuts off it  ) would fix such issues but there you go! Just goes to show that diesels really do prefer to be used hard!  

I didn't in fact thrash it for most of the journey it was on cruise, recon it just needed to get thoroughly hot to burn off the soot!