Hey all, I have an 08' Fit with 160,000 miles and a manual transmission. She's been been acting funny for the past few weeks, so my mechanic suggested a valve adjustment based on the symptoms and felt a dealership would better serve me.

Symptoms: Loss of power after a cold start, shaky idle with A/C, and overheating light.
Went to the dealership, got a valve adjustment, water pump and drive belt, and a new thermostat. (Based on price, I understand the stealership comments now!)

After I picked her up, she improved slightly but still felt a little off in 3rd gear. The belt made a noise afterwards but finally went away after awhile. 300 miles and a week later, she throws the P0420 code. I was already going to take her back to the dealership to get her re-checked but they're saying that the issues are completely unrelated. They said the catalytic converters showed no issues at the time.

Of course, the dealership was condescending and service advisors and managers have been difficult to deal with. I'm dropping her off today and hoping to hear something "when they have availability to look at her".

So my question is, has anyone experienced a P0420 code after a valve adjustment? Is it possible that they messed up the adjustment and it somehow affected the catalytic converters or something to throw the code? I'm expecting them to come back with "You need new catalytic converters and we did everything right" but it just seems suspicious to me.

 

Please note that internet diagnostic should be taken with grain of salt but here is my theory. The catalytic converter started disintegrating and created exhaust back pressure (aka potato in exhaust) with the symptoms similar to out of adjustment valves plus overheating of the engine. So your mechanic diagnosed your car as valves out of adjustment and did not look on catalytic converter.
PS. The water pump can leak and make a noise but seldom cause engine overheating (as long as you not run out of coolant)

 

Good theory above. Here are some of my thoughts...

At 160,000 miles, the car would need a valve adjustment if not done prior, so it's good they did that.

The belt in these cars is not self tensioning. It is normal to need them adjusted after a couple hundred miles of break in. Do it now before it causes undue wear. Ours did the same thing after a new belt was installed. I had re-adjust.

Overall, it's good they did what they did and the belt just needs a quick adjustment. That being said, I'm betting the doctor J is correct about the misdiagnosis. You may need a new catalytic converter. I'm sorry to say, they AREN'T cheap.