Two Questions

I have the following two questions:

1) On an '93 GM withg ABS and Traction Control I am getting a "66 - Pressure Switch Circuit Failure". Is it the Pressure Switch or is this some sort of general code? If it is the Pressure Switch, where is it and does anyone have repair instructions?

2) Also getting Check Engine Light Codes (only at highway speeds and sometimes only) of 332 and 337 EGR Flow Insufficient and EGR Sensor Above Max Limits. Does the EGR need replacement or is it the PFE Sensor (or both)? Perhaps only a cleaning of the EGR area under the Throttle Body elbow??

The pressure switch is a 33 step test to completely diagnose it. It can also be the fluid level indicator or the brake travel switch. It is not a quick and easy test. The pressure swirtch is on the ABS Hydraulic Control Unit. If it has continuity to ground, you need to replace the reservoir on the HCU. If there is no continuity, repair the wiring to switch. That is the short and sweet test for the pressure switch.

As far as the EGR code, you are on the right track in all accounts. Check for voltage going to the DPFE/PFE sensor. There should be approximately 5 volts. The return wire should have a lower voltage, under 1 volt. You need to check for vacuum at the valve also. Vacuum on the valve will change voltage on the DPFE/PFE sensor. A good cleaning of the passages is always a good idea if you are not sure of blockages. The EGR valve will be the last thing that will cause the code. Usually the carbon build up or ther DPFE/PFE sensor will cause it.

Would the DPFE be between the throttle elbow and the firewall? It is difficult to see back there but it is the only item there. There is a black object, just above the EGR disk so perhaps that is the EGV?

The DPFE/PFE will be a small black and silver box that is attached to a hose that comes off the tube. The sensor is located below the vent valve on a bracket bolted to the back of the throttle body. Go here (http://autozone.com/az/cds/en_us/0900823d/80/19/30/56/0900823d80193056/repairInfoPages.htm)and it lists all the componets except the DPFE/PFE sensor. A little more searching of the site may yield more results.

The ABS Light has NOT come on in the past week or so. I would think that would indicate a electrical short as opposed to a bad part. I believe there was a TSB referring to a problem with the ABS wiring near the ABS Computer by the radiator. Any thoughts about this?? MB

I believe this might be on the TSB you are talking about. It is TSB 93-10-1. Here is a picture of where they say is a good possibility for wiring damage.

http://usera.imagecave.com/way2old/mgmabs.gif