1990 240 CO reading too high to pass emmissions

ilike240 · Post by **ilike240** » 15 Dec 2011, 17:18

Hello, I bought a 1990 240 and the car failed emissions due to CO being too high (other parameters were o.k.). Car is showing code 1-2-3 first (temp sensor) followed by 2-3-2 (Lambda). How likely is it that a bad temp sensor is causing it to run too rich?

Here is some background. Car has been very well maintained (plugs wires etc. etc. all gaskets etc.) but has 271k miles. Engine has tons of power. Idle is good but not perfect maybe has tad bit of a miss at times.

So far I have tried cleaning throttle body, idle control valve (I think that's what it is) and replaced a cracked vacuum hose. Tried checking for vacuum leaks with carb cleaner but couldn't find any. Air filter is pretty darn clean. Cleaned MAF. Tried running fuel injector cleaner and no change. Disconnected battery and code comes back in about 3-4 minutes whether engine is cold or warm.

What do you guys think I should check or try? Any way to test the coolant temp sensor? Other ideas?

Thanks for any help!

Post by **JDS60R** » 15 Dec 2011, 19:44

very likely as the car enriches the mixture when it thinks the car is cold. It uses the temp sensor to perform this so it logically follows that if the sensor or sensor wire is damaged the computer may be getting a false reading.

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Post by **billofdurham** » 16 Dec 2011, 11:25

ilike240, welcome to Matthew's Volvo Site.

You can test the coolant temp sensor with an ohmmeter. Values are attached:

240 Coolant temperature sensor test..pdf: (177.66 KiB) Downloaded 175 times

Values for the '90 model are the same as for the '89.

Bill.

ilike240 · Post by **ilike240** » 16 Dec 2011, 17:51

Thanks for the replies. Bill I guess I saw your post too late as i just bought the new temp sensor and installed. Thanks for posting that though. That was the kind of thing I was looking for. I was surprised to see the Bosch sensor in stock at the store down the street so I went ahead and bought it. The bosch sensor was $36 and the aftermarket is around $15.

After installing, the light in the dash stayed out even after half an hour of driving. Also the idle is much smoother now. So I would guess this solved the problem. As said above, the sensor must have been giving wrong values causing it to run too rich. As I understand the OBD, the fact that it gave the temp. sensor code first means that is the primary problem. The second code, the lamda, is the secondary problem. That certainly seems to be the case so far.

It's amazing to me that this car has 270k and the engine sounds as smooth as when new. Also tons of power. They should have just kept using this same engine forever, even today. Why change when they have something so bulletproof?

Post by **billofdurham** » 17 Dec 2011, 11:32

Good to know it seems to be OK. The Lambda code would be set as a result of the temp sensor failure. Thank you for the update.

Bill.

ilike240 · Post by **ilike240** » 19 Dec 2011, 07:00

The engine light came back on Yesterday. Same code 1-2-3. I unhooked the battery and restarted and the code came back after a minute or two. I disconnected the temp sensor and unhooked the battery. Then reconnected both. The code came after about 15 minutes.

So what else can i do? Is there something else that would thorw the temp sensor code or do I need to try to redue the wiring to the temp sensor? That is a pain to get to so I'm reluctant to do that. Thanks for any ideas.

Post by **billofdurham** » 19 Dec 2011, 11:53

I am curious as to why you disconnect the battery to erase the codes. It is much easier to use the OBD unit to do this. Every time the battery is disconnected the computer has to go through a relearn procedure which can cause driveability problems. The attached is from a Volvo publication on this subject:

240 computer relearn procedures.pdf: (621.49 KiB) Downloaded 228 times

Have you tested the new sensor? It is not unknown for a new part to be faulty.

Bill.

ilike240 · Post by **ilike240** » 19 Dec 2011, 16:48

Very interesting on the computer re-learn procedure. Thanks for posting that. I never thought about the relearning process. The reason for disconnecting the battery is that is what it says to do to erase the codes on the last page of the OBD instructions.

Post by **billofdurham** » 20 Dec 2011, 12:21

It just goes to show I didn't check that one properly.

I have added to the original post the method for erasing the codes. Thanks for pointing it out.

Bill.

ilike240 · Post by **ilike240** » 21 Dec 2011, 17:53

Thanks for helping with such excellent instructions. I don't know how many mechanics places that said "if it's not OBD2 I can't work on it" If they only took time to find sites like this they could learn to do more than simply scan the codes and replacing things via trial and error. Anyway this site is a fantastic resource for us DIYers and is MUCH appreciated.