Check Engine light on/off seemingly dependent on temperature?

Maintenance/Repairs
1

hi experts. i have a vw jetta 1.8T w/ 130K miles on it. recently when the temperature dips below, say, 35F my check engine light goes on and basically stays on each time i start the car until the temperature rises to say 37/40F. then it turns off. this is honestly the only factor i’ve noticed that makes a difference. i’m in NY, so its been dipping around there for a couple weeks.



any clues as to what i should look for? and naturally, how worried should i be?



note: did 120K service 5K late, so in theory everything was checked 5K miles ago.



thanks alot.

2

Even if the light goes out, the trouble code remains in memory. Get the codes read, and post them here.

As someone said earlier, the CEL is like a kid in class raising his hand. The computer has detected a problem, and set a trouble code. Once the code is read, the problem can be tracked down and fixed. This could be a really cheap fix, like needing a new gas cap or a sensor going bad. Get the codes read so you’ll know.

3

That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

Regarding warning lights:

  1. if the coolant temp light comes on, shut off the engine ASAP

  2. if the oil warning light comes on, shut off the engine ASAP

  3. if a FLASHING MIL/CEL comes on, shut off the engine ASAP

    ASAP means driving to the berm of the highway right now and not waiting for the next exit.

But if the MIL/CEL is not flashing, then it’s not an urgent indicator.

4

thanks to you both. i’ll track down one of those two stores and post the codes up here.

5

Here is what my readout from autozone said.

Code: P1136
OEM Brand W

Defintion: Long Term Fuel Trim Add Fuel B1 System Toc Lean
Explanation: Failed MAF
Probable Cauuses

  1. Low fueld pressure
  2. vacuum leank on engine
  3. failed N02S
6

Ahhh. I like the vacuum leak scenario. Especially with the cold. Rubber will constrict with the cold, and could reveal hidden cracks. This will allow air into the intake that by-passes the Mass Air Flow (MAF) sensor, and causes a lean condition. Check all the vacuum lines and air intake lines.