NEED HELP Transmission and Headlight Issues

[jessiewebster]

3 local mechanics were "stumped" when I took my 2004 Envoy in to be looked at. It started to feel like it was not getting enough power occasionally when I was driving between 55 -65 mph, the RMP's would slightly fluctuate, and sometimes it started to shake when it was struggling. One shop replaced a O2 sensor and spark plugs and also replaced a starter that was bad, the other shop drained and refilled my trans. fluid. Both places said that should take care of the problem, and there were no codes coming up a scan, but its still doing the same thing. My trans. fluid now smells burnt and is dark. I thought it was/is a trans issue but one of the shops thinks its a misfire issue and I need a air pump replaced. Does that sound right to you all? Ive had it for 6 years and have never replaced or had to repair the transmission... Trucks got 175,000 miles on it & Im wondering if I should put more $$ into fixing it.

One more question- after left the shop that replaced the spark plugs and O2 sensor my low beam headlights no longer worked. The high beams work and I have daytime running lights but no low beam lights. Any idea why or how I can try to fix that myself?

Thanks y'all

 

[dmanns67]

Do you know what spark plugs the shop installed? Should be AcDelco 41-103 assuming you have the 4.2L I6. That is the only spark plug that should be used on the I6. Using different spark plugs than the ones listed above can cause issues.

Your profile says that your Envoy has a 2.8L I4 which is not correct unless you did an engine swap.

As far as the misfire goes, if you had an issue you would see a general misfire code of P0300. If you get a P0301 that is tied to cylinder one, P0302 cylinder two, etc. Have you ever replaced your coils or are they stock?

Low beam headlight issue is common on our platform. Most of the time the issue is the headlight relay which is located in the fuse box in the engine bay. The fan clutch uses the same relay. You can swap the fan clutch relay with the headlight relay to see if that resolves your issue.

Air pump, are you talking about the secondary air injection pump? That should be throwing a code as well.

 

[jessiewebster]

Thanks! I didn't do an engine swap....I kind of guessed & thought that was what my envoy had.

Ill check the sparks plugs. I didn't ask when I was as the shop. Could that cause the headlight issue is the wrong plugs were used? When I dropped it off the headlights worked and when I picked it up after the O2 sensor and plugs were changed, and drove it later that night, I realized I had no headlights. I brought it back to the shop and they said it could be a 100 things causing it.

Not sure about it being a air injection pump. They just said there was a bad air pump.

 

[AtlWrk]

How did they drain the transmission? There's no drain plug (unless you or a previous owner added one) so they either pumped it out the dipstick tube or dropped the pan (or used the trans pump itself to pump out the through the oil cooler line--though that's more of a home mechanic's trick).

If they dropped the pan did they inspect it for signs of trouble (metallic flakes, clutch debris, etc.)? New filter? The fact that the new fluid is already dark and smells burnt indicates a serious problem that needs immediate attention (that or they just said they changed the fluid). Also, a simple drain and refill replaces less than half the fluid in the trans (the whole tranny holds about 11 quarts but a pan drop only gets you maybe 5) so the dark/burnt condition may just be from the fluid that remained. Either way it still needs to be replaced--things go downhill fast for a transmission with sub-par fluid.

How much fluid did they add (how much did they charge you for)? What was the condition of the fluid they drained?
Was it at the proper level before and is it now?

The RPM fluctuation at highway speeds is likely the well-documented torque converter clutch (TCC) valve starting to leak causing the transmission to slip in and out of lock-up. It can be fixed with a kit you order and have a trans shop install (or do yourself if you're so inclined for a very messy job).

The lack of power can be a number of issues from misfires (though if it was that bad I would expect a trouble code) to a clogged catalytic converter to the transmission slipping to fuel injector issues, etc. One thing it definitely is NOT is the air pump. Would be curious to hear the diagnostic logic that came up with that.

The only way I can see the headlight issue being related to the work done is that they (hopefully) disconnected the battery. If the relay was on its way out that may have been enough to finally kill it. As previously stated, temporarily swap it with the fan clutch relay (same design). If they start behaving normally than you know you need a (AC Delco OEM only!) replacement. Otherwise I'd search the forums for headlight issues (been discussed many times) for more diagnostic help.