Hey there guys, just took the car out for a blast and when i got to 4500 revs the CEL came on and the car felt like it had hit the rev limit. Just checked the code and it's 45. Does anyone know what this is? I tried searching but I'm on my phone and it didn't work, sorry!

Thanks
Wayne

 

CEL 45 is MAP sensor, which makes sense considering the circumstances of when you got it - your engine either over-boosted very briefly, or at least the ECU thought it did, and cut the fuel supply to protect it from damage, giving you that rev-limiter effect.

Best to drive off boost until you can get it properly checked out.

 

Cheers for that. What is the MAP sensor thou?!
Think I'll use my bike for work till I get it checked over! Don't want to break it!

 

MAP = manifold absolute pressure
It's what the ECU uses to work out how much boost (or vacuum) the intake is operating under, in real-time.

 

Ah is that all the stuff on the left side of the engine bay? Is it just a matter of swappin it for one off another car?

 

Wayne
I honestly don't know how prone to wear or failure MAPs actually are, but as a general rule I think you always have to be slightly cautious with any of the sensors about some other component or combination of factors giving a false failure-reading. In any case, MAP sensor is just one of the components in the engine-bay where you said.

From your avatar I'm guessing your car is a classic of some sort, but more details on model-year, engine-type, modifications, other symptoms and so on would help. Ultimately you also have to remember that internet-based diagnostics is no substitute for a hands-on look by a specialist or someone who knows Imprezas very well.

 

Hey mark cheers for the reply. The car is a MY96 version 2 STi. It has a forged engine which has done 15000 miles, it has a HKS induction kit on it, vent to air dump valve and a turbo back exhaust.
For a while the car had had a very lumpy idle and struggles to pull away at low revs. Is there anyway I can test the MAP sensor, like with a multimeter?
Thanks
Wayne

 

Wayne
If your car was mapped for the induction kit and dump-valve, your mapper is probably the best person to speak to about the problem. On the other hand, if it wasn't mapped for them it could well explain why you've had the CEL and the lumpy running in the first place, as these are both modifications which are known to push a standard ECU beyond the limits of what it can properly compensate for. A definite worry in this case would be the possible long-term consequences, which can often include premature MAF (mass air-flow sensor) failure and generally poor air-fuel adjustment, both eventually leading to likely engine death through prolonged DET and lean-running.


So far as testing a MAP sensor is concerned, it can be done but it isn't easy. You need a vacuum pump with an accurate pressure gauge as well as a multimeter, so cost-wise if you don't already have the tools not far short of a brand new sensor.

 

Hey
Cheers for the info mark. Car has been into the garage and they are sure it is the MAP sensor that has failed. Problem is subaru want £413 for a new one when i just called them!! Gonna pop down the breakers later and see if i can get a 2nd hand one! Does it have to be off a version 2 or will any do?

 

Wayne
I know others have used later model MAP sensors on v1 or v2 cars, because they have higher upper limit which allows for running more boost, but I'm not sure if the connector is the same size and shape.