94 V6 has been back on the road for about a month after an engine rebuild (and more). I've put about 900 miles on it and odometer now shows 131k miles.

From the moment i first started the engine it has run beautifully. There's the noise transmission issue that I'll eventually handle (I hope) by installing new mounts but that's minor.

The Service Engine Soon (SES) lamp came on during the first test drive and a scan showed EGR valve codes (2). Okay, fine, I'll get an EGR valve. A week ago I got 2 used ones and installed the best looking one. No SES appeared following a short test drive.

This past weekend, however, I made a trip of about 120 miles and had the scan tool hooked up the whole time. EGR solenoid 3 code came on as soon as I hit the highway. It was interesting to watch the PCM command the various solenoids on and off as I drove. EGR solenoid 1 comes on immediately off idle. As you accelerate number 1 turns off and number 2 briefly comes on. Then 1 and 2 are operated together at secondary road crusing speed. As soon as you let off the gas they both turn off (no EGR at idle).

What's weird is that the EGR solenoid 3 code shows up without the solenoid being activated. You can be cruising along at a steady speed, maybe 35 mph, and *boink* the SES light comes on and theres the EGR code again. No solenoid 3 activation ever requested (according to the scan tool). Clear the code, the SES lamp turns off, and seconds later it comes on again. Only this one code is stored.

Weird, but it gets weirder.

So I'm cruising along at maybe 60 mph, and scrolling through the scan tool's various menus, seeing what I can look at. I realize that I haven't looked at the *transmission* control data. Lots of interesting stuff shows up regarding pressures, solenoid duty cycles, atf temp, and *what!* there are *7* codes stored! WTF? I look at them and see low TP sensor voltage, loss of vehicle speed sensor data, bad EGR solenoid 3, right bank rich, EEPROM error, TCC solenoid error, and one more I can't remember.

I figured that these codes had been in there for a long time, possible accumulating for years, so I cleared them. Great. A minute later I look and they're back! All 7!

Now I start to look at the TP data, the TCC behavior (I can feel it come on and off), etc. Everythng looks fine. I can see the speedo working so what's with the VSS code? I clear the codes and, again, they come back!

I return home and sleep on it.

I got to thinking that I *have* noticed a slight hesitation when you first give it throttle from a standing start. Maybe the TP sensor has a bad spot off idle (pretty common) and that's causing the hesitation and also making a weird combination of conditions that result in these codes. So I go to my parts stash, pull the TP sensor off my junk 3.4, and install it. Despite what I've read the TP sensor *is* adjustable and that initially caused some problems for me. Anyway, a test drive shows that the hesitation it gone. Great, I think, problem solved. I take the kids to school (about 10 miles round trip) and no SES, no transmission codes. Fixed! Awesome!

When I pick them up later we go for a longer drive (faster roads) and the SES light comes on. Not fixed. Not so awesome. Under engine controls only the EGR code is present. Under transmission all 7 of my friends are back.

So does anyone here know why some codes show up under engine and more under transmission? EGR code under engine turns on the SES but TP sensor, right bank rich, etc. under transmission don't? That can't be right.

My first thought is bad PCM. I pulled a spare from a 94 V6 with auto trans at the U-Pull-It a couple of weeks ago. I think I'll install it this morning and see what happens.

 

I took the kids to school this morning. No SES there and no SES back. Got home and checked for codes; the familiar 7 were there for the transmission. Whatever.

I disconnected the scan tool and swapped PCMs (mine out, junkyard 94 in, exact same part number) and hooked up the scan tool. Turned the key to run only to view data in the "new" PCM. I did not crank or start the engine. Checked for engine codes -- none. Checked for transmission codes -- the same 7 codes were there!!! WTF? Why would the PCM from another car have the same 7 codes present? I cleared them but I'm sure they'll be back. Oh yeah, they'll be back. And I'll be ignoring them.
The only thing I can think of that would cause this weird situation would be if the car had separate engine and transmission computer. Not so, right? All the books I've looked at say that the PCM handles both engine and trans functions.
I'm stumped.

 

you need to test the vss on the transmission. vss produces ac current, i think .5 volts it should pulse when the driveline is turned. im still lookin for the test, had a long day so ill have to look tomorrow. also need to check all wires you can get to for shorts.

 

I'll check the VSS next time I have the car on a lift. One other thing I should note: according to the scan tool my cluster reads high.

The tach, which shows about a 900 RPM idle speed, is apparently 200 RPM high.

The speedo reads 4 or 5 mph high. This is backed up by readings on the side-of-the-road radar displays they use around here in construction zones. When my speedo says 65 mph the radar things consistently read 60 or 61 mph.

 

see if theres anything here that will help.

 

Thanks.
Any chance you could post the trouble tree for code 77? I'd like to see the conditions required for that code to set.

 

 

Ah, thanks, the description makes it quite clear how the code sets without driving conditions actually call for EGR solenoid #3 to be activated.