Diagnose this

[Nyquist]

This is a current and on-going issue with a friend's car. They approached me today at 9 am and wanted me to take a look at their 2003 Impala with a 3.4L. The LIM gasket was just replaced along with the transmission flushed. The transmission pan gasket was leaking, so they had the place re-do it under the 12 month/12,000 mile warranty that comes with the shop's work. The engine oil was full when I checked it.

His wife drives the car every day on the interstate around 65 mph. She's been complaining about it shifting a bit rough and a lack of power.

I drove it and the throttle feels a little touchy, but that could be because I'm not used to it. It also shudders when it shifts, and this is much more pronounced under constant throttle and driving up hill, so load is increased.

I plugged into it, and there are no traditional trouble codes--no lights on the dash.

There is a current enhanced, manufacturer-specific code of P1189 which translates to "Engine oil pressure switch circuit."

This same P1189 is also present in the "Fail Since Clear" category along with a P1811 which translates to "Long Shift & Max Adapt" code.

Both the P1189 and P1811 appear in the history codes section too.

Thoughts? Debate! Thanks!

 

[parimento1]

P1811 means your transmission is slippinga bit and the computer is trying to compensate by increasing line pressure. However, it has maxed out on its ability to compensate and has thrown a code. See if these codes are in all the shift circuits or just for certain gears. It might be a clogged circuit, leaky bushing, anything really. Have it checked out by a tranny place. Don't use trans fix unless you just want to fix it enough so no one will notice on a trade-in.

 

[beast3300]

Alot of times a P1811 means the 4T65 has had it. As far as the P1189. Alldata says check wiring, if good, replace sensor. If it still doesn't fix it, replace PCM.

 

[dwendt44]

Vacuum leak?

 

[Nyquist]

Here's my list of things to check today since I got more information out of the couple:

• No fuel filter in the past 45,000 miles.
• No known replacement of plugs/wires.
• After the transmission was flushed, they also had to have an axle seal replaced that started leaking.

One thing that crossed my mind last night on the initial test drive is that it's possible there may be an under-lying engine issue that is causing the odd behavior from the transmission since it seems that a lot of the issues in this platform were addressed after the 2002 model year.

I'm going to run some tests on the MAP and MAF today to see how much that changes the idle along with taking a look at those plugs/wires.

I figured it was also possible that there may be a sticking valve in the transmission.

I'll be able to find out more today since visibility isn't 400 feet like it was last night with all the fog we had.

 

[OVERKILL]

I wonder if the shop used the right fluid.......

 

[ls1mike]

Originally Posted By: OVERK1LL
I wonder if the shop used the right fluid.......

I was going to ask that, also how many miles on the car and how many were on it when they did the flush?

 

[Nyquist]

Flushed around 110,000 miles. The local Chevy dealer did it, so I'm assuming they used the correct fluid since everyone and their neighbor has Dexron III.

 

[ls1mike]

110,000 Hmmm, had it been serviced before that?

 

[Nyquist]

I'm 80% sure I found it. On a drive today I shifted it through the gears and there was no slippage. It felt a little labored on the shift, but no RPM spike that can be associated with a slip. I even shifted it from OD to 3rd and from 3rd to 2nd. It didn't wonder back and forth. Rather it had fairly solid shifts under that situation.

I did feel the shudder when it wasn't shifting today, and since there were no weather issues I could investigate further.

The shudder did not come in a constant frequency for a speed, so that would tend to rule out the torque converter.

I then started focusing on the engine itself. The more I got it to shudder, the more it felt like it was coming from the engine especially the ignition. We pulled into my garage where it was a little dark, and found that the plug wires were occasionally arcing through the plug boot to the cylinder heads.

It looks like a simple tune-up with plugs/wires and a fuel filter may solve this one.

Happy days!

 

[ls1mike]

Good on ya! That is as an easy fix! Hopefully that clears it up.

 

[mechanicx]

Good job. Checking the ignition system was a very smart move. Those back plug wires are tough to get to though i think. Might want to add a big bottle of Techron in thegas for good measure.

 

[Nyquist]

I'm not doing the tune-up myself though. Those plugs are original from the sounds of it. I'll let someone else risk pulling the threads out of the cylinder heads since I don't have insurance for that. I did save them over $200 on diagnostics though.

 

[saberz]

It's the cat, without a doubt.


My 01 Impala had 72k on it when the car literally through the same error code and felt like molasses when trying to accelerate. I thought the trans was going but took it to the dealer and it turned out to be a clogged/failing cat. Cost was free as its an 80k warranty on the cat.

Car ran like new afterwards, no more code. The car being sluggish was straining the trans due to poor shifting/quality. I could literally go WOT and go 25 mph tops and it took awhile to get there.