I had been trying to chase down the cause to my p1237 code for over a year. Jumping on the forums did nothing for me, being that none of the OPs would chime in once they had fixed the problem, and state the remedy. Well I'm going to post mine--for poor saps like me to stumble upon.

Code p1237 is "secondary upstream manifold air pressure sensor low input" and causes a SES light.

My fix: The sensor next to the airbox (upper left) had a severed wire. Simple as that. Bridge the gap with a new connection and the code disappeared.

Now your fix may not be as easy as mine, but this should be your very first step in your discovery.

Good Luck.

 

Kudos for posting the solution. Good to know, and useful to understand that "low input" means nothing is being received from the sensor

 

Mind posting a photo of the actual sensor? My light has been intermittent. It comes and goes as it pleases, but its only been doing it for a week now.

 

It's the Secondary Upstream MAP sensor. Looks like this:




Light came on again, this time the Vacuum hose on ByPass Valce (BPV) was disconnected. The BPV is located on the driver’s side of the engine, beneath the intercooler.

 

Thought I'd document my experience here.

Kept getting intermittent P1237 and occasionally other codes (P0300 etc.). One time my car (2003 R53 MCS, 70k miles) went into idle-only limp mode when I was testing getting on and off the boost in 2nd gear (normal operation resumed after I restarted the car).

Replaced both the MAP and TMAP sensors; no dice.

After some more research I replaced the stock compressor bypass valve (CBV) with one from Detroit Tuned. Fixed the CEL, loss of power, limping, throttle response problems.

Today I took apart the old OEM CBV. (See attached photo.) Turns out the spring had snapped clean in two!

 

Thanks for posting this. I'm dealing with a 1237 myself at the moment and there's not enough good info out there. How did it feel when you operated the valve? Did it feel like it was springing back at all on it's own or not at all?

 

One tip...
The cold side r53 map is the same part as the r50 tmap...it just does not use the temp...one less wire in the bundle... Then the hot side t-map on the front is a r53 specific part...they look the same, BUT ARE NOT INTERCHANGEABLE.
MY EXPERANCE....
I changed the cold side one...car ran good for a few miles, then did the hotside t-map, all was fine.
Some folks swear that the tmaps NEVER fail, but I know 3 or folks on another board that have had them fail...
Buying them from a online source like massmini parts (aka mini of Peabody MA, or their sister dealer mini of Bedford NH) drops the price of the OEM to match the aftermarket ones...so I'd buy OEM...dealers will have to order them...about a 3 day wait...and about +50% more than the two mini dealers that do online parts sales....
Forget the code I got, but I got a limp mode occasionaly, and a near instant DSC warning after a reset of the odb2...

 

Thanks Zippy. What did you mean by "then did the outside"? You replaced the TMAP too?

I never considered not going OEM with the MAP sensor. They're relatively inexpensive enough (unlike $500 vs $100 for a non oem axle).

I myself did get limp mode (and I'm pretty sure the car even completely stalled out one day but I think that may have come from my 2 year old oem coolant tank pissing coolant all over the coilpack wiring) but it's hard to say whether it was from that or more likely the misfire with the old wires I was running.

 

Sorry...auto correct...should have said hotside (did it again...had to go back and fix it!!).
I would have done them both at the same time...would have save some grief...found another shop that said (on the other board) that said they swap them in pairs...think they were like 69-89$ each for OEM. Funny, the track folks, the founder of the site, Nathan (also a former mod here) and a couple other folks all had failures...guessing highly boosted cars tend to make the t-map or map run at or near to its limits...
A google search did yeild a 20-25 page PDF doc from the BMW/mini this on how to troubleshoot the tmaps, voltages, etc...not sure of the address, but think it was at BMW world...

 

It seemed to operate somewhat-normally as in it would resist opening and spring back closed, but I did notice it seemed a bit slow about springing back closed and it felt like the last little bit of the range of motion before closing was a bit "soft" like it could possibly stick open a bit. I also wondered if maybe the sharp tip left by the break in the spring might have pierced a hole in the diaphragm, but this doesn't appear to have been the case.

 

P.S.
Crazy...one thought...
The hotside t-map is easy to get at..on the front of the intake by the radiator shroud...try cleaning it?
Just for giggles I DID swap the hot and cold for a few moments...
What I found...just in the driveway for a few moments..only to 2500 rpm or so, no boost...did not want to run the sensor out of limits...
The DSC light went out...car would not idle or run without gas pedal input below maybe 800 rpm (guess) but the fact the DSC light STAYED out leads me to believe the temp part was out...
I did find info about guys who did turbo conversions state if the cold side is not installed, the computer CAN COPE and car runs OK...since it is only sensing ambient psi and that does not vary as much..a bit of a guess...still...look at the wiring...easy to trace both since it is so short to inspect...maybe it was s just pinched? Good luck!

 

thanks for the follow-up

Al

 

Yup. I have the document but unfortunately it references using DISplus computer to do the diagnostics.

For anyone interested, it can be found here:

http://www.bmw-planet.com/lib/mini/E...20OVERVIEW.pdf

 

I had the exact same problem, although my solution ended up being different. Problem? P1237, sometimes p1238, sputtering, random backfires, limp mode sometimes.

Change the map sensor, no solution. Change the team map sensor, no solution. Bypass valve was replaced with a Detroit tune valve three months, upon inspection it looked fine. Smoke tested the intake system, found a big leak the vacuum line on the bottom of the bypass valve. The bypass valve itself was fine, so when I pulled it out and looked everything seemed normal. Line directly below it was cracked in two places. Picture below. that line was replaced and I was still getting p1237. And mini master tech told me to put back in the original map and tmap sensors, and that should clear the code. It did. The aftermarket sensors don't always give the correct code readings or clear in the ECU properly.

 

I have the same code. But here's the weird part. I cleared the codes, went back in and there was already a P1237 pending! The only thing happening at that moment was the key was on! So does this look more electrical (like the OP found)

thanks

Bill