Help with CEL - P1237
 

Hello,

I have an R52 that suddenly developed engine trouble. I was able to drive to a mechanic who pulled the code and I got P1237 - Secondary Upstream Manifold Air Pressure Sensor Low Input. When I drive the car the engine speed is not smooth and it will periodically cut out/stumble for a split second. Barely registers on the tachometer but you can feel the hesitation & lack of smoothness. I just did another test drive and the problem was less with a cold engine and then started to act up more as it warmed up. At one point it cut out so the throttle no longer did anything, but it appeared to stay idle. I had to shut the car off and back on and then it was back to the normal stumble behavior and I just limped home with it. Power seems to be unaffected throughout the rpm ranges. I have read up with this and people seem to be focused on bypass valve, vacuum leak, or one of the two map sensors. In regards to service this Mini had a throttle body replaced 4 years ago or so and I just had a radiator replaced a few weeks / few hundred miles ago. The car had been running fine and then all the sudden the problems above immediately accompanied with the check engine light.

How do I got about troubleshooting/fixing this?

Thanks in advance for any insight,

- Mike

There are two MAP sensors and your code points toward one of them.

Where the TMAP and MAP are located:
https://www.northamericanmotoring.co...-location.html

What the code means:
https://www.northamericanmotoring.co...1237-help.html

Thanks Whine not Walnuts! Would you recommend the next step here to go ahead and replace the TMAP sensor based on the behavior I described? It appears to run around $100 so I wanted to check that this was the most reasonable path before replacing parts that may not be the issue. Thanks!

Long distance diagnosis is like throwing darts at a board blindfolded. A MINI shop will have Insta software that has test templates on how to determine what is wrong. If you are not comfortable with electronic testing/trouble shooting and want to gamble on buying a new sensor . . . . . . .

I have Ista but if I did not I would probably do some shopping and buy a MAP, not TMAP and install it.

Hi all,

I just wanted to follow up on this, may help someone in the future. After realizing this would be a part replacement guessing game for me with my limited mechanical ability, I brought the car to a reputable local mechanic. The diagnosis was faulty supercharger bypass valve. I had them replace it and I've put just about a hundred miles on it since getting it back and it is running great again. Case closed. Special thanks to Whine not Walnuts for the honest guidance.

- Mike

The Ista program not only reads the code but also provides possible causes and the procedure to determine what component is faulty. There is a "Tool" they reference relative to testing the MAP/TMAP. There may be a post somewhere on what voltages and or ohms one is suppose to see across the leads.