Ok so im relatively new to this model its a 94 3.4 with a 4l60e, had it about 4 months, first thing I noticed is that it's running extremely rich and when driving if you go over 50 mph and hit the brakes the ses light comes on but still drives just fine. I've tried scanning for codes but it won't pull the codes. Hopefully someone can help with this!

 

To pull codes on your car you need an OBDI scanner. A plain code reader won't work, and the codes cannot be flashed.

 

More than likely it's the egr valve, mine has been that way since I replaced the motor 2 years ago. I've replaced the egr twice and still get a SES when i go above 2400 rpm in 3rd or 4th and then go back to idle. I've tried cleaning and egr passages and still to good. I've just learned to live with it.

 

I did a complete rebuild of the 3.4 in my 94 last year. The car wasn't driveable when I bought it so I don't know if it had the problem before.

Driving on local roads at speeds under 40 mph or so isn't a problem. I drive like that for a month and the SES light won't come on.

As soon as I hit the highway the SES light does come on and the code for EGR solenoid #3 sets.

I've swapped in 3 other EGR valves from junkyard cars. Same problem, and they can't all be bad. I swapped in the PCM from another 94, 3.4, auto car. Same problem.

I've measured resistance of the wires between the EGR valve and the PCM. No problems.

Some service manual reading reveals that the PCM tests the EGR system during engine operation by waiting until road speed reaches a certain value followed by closed throttle conditions. At that point manifold vacuum should be at its highest.

Then the PCM operates each EGR solenoid individually and in various combinations, monitoring the change in manifold absolute pressure each time. When the PCM gets a result that it doesn't like, it turns on the SES light.

So I changed the MAP sensor. Same problem.

Then I gave up.

EGR solenoid #3 operates the largest EGR pintle so the problem must be that the PCM doesn't see a big enough pressure rise.

I'm thinking partially obstructed EGR corrugated pipe or cast iron tube that the valve sets on.

Either way it is too big a PITA for me to deal with it now. Maybe this winter.

 

Try the throttle position sensor, I've replaced the egr valve, o2 sensor, map sensor, and the last thing I replaced was the tps and since then it hasn't come on no matter how I drive it, hopefully this helps

 

I've replaced it already, separate issue, and it still does it.