Dreaded SES light
 

Hello all. I have a 93 Full size 4x4 Blazer. New to me, but has 157,000 on the clock. The motor is fresh with about 30,000 on it. My SES light comes on after about 20 miles. The codes it spitting out are talking about the EGR fault.(#32) and a fuel pump relay low voltage(#54). It does have a pretty rough idle after it warms up so I have been thinking I have a vac leak somewhere. But couldn't not enough voltage to the fuel pump cause the same symptoms? I can kill the engine and the light will go out until I drive for another 15-20 mile then it comes back on. I also have an aftermarket Excalibur alarm on it. My key fob is shot so I never arm or disarm it. My other question is does the alarm system splice into the fuel pump electrical circuit to effectively kill the pump upon system arm? I know nothing about alarm installations. Maybe that's the reason for the low voltage to the fuel pump relay? Any suggestion will be greatly appreciated. Thanks

Anyone?

Having an aftermarket alarm system makes it very difficult to really diagnose your problem. That could be the cause of the issue, could be a contributor, or could be completely unrelated.

The description for code 54 states that the PCM monitors the status of the fuel pump circuit at terminal B12 and uses it to compensate fuel delivery based on system voltage. This signal is used to store a DTC if the fuel pump relay is defective or if the fuel pump voltage is lost while the engine is running. There should be 12V on the circuit for at least 2 seconds after the ignition is turned ON or any time reference pulses are being received by the PCM.

Sounds like something is causing an intermittent 12V signal to the PCM B12 terminal.

I have a similar related problem: My engine light, not the SES light is on, the scanner says that I have a problem with a rich mixture in the oxygen sensor at the back of my blazer, 96, 4.3, 2W, would cleaning the EGR valve and the MAF sensor help this problem? Thanks,

Actually, your problem is quite unrelated since there is very little in common between the two vehicles. Please run a search on your problem. If you cannot find the answers you seek, you can reply to the thread I moved your first post into rather than drag this topic off on a tangent. Thank you.

I thank you for the diagram. I am kind of under the impression that the Excalibur alarm might actually be suspect here. It is one of those dealership installed alarms I think. I remember back in the day when these trucks were new on the lot with them. I think that it taps into the fuel pump circuit somehow and maybe the contacts on the relay of the alarm may possibly be causing this. Would this low voltage problem cause the misfire condition at idle? The motor runs strong above idle speed. But when I am at a red light with my foot on the brake, it's idling at about 250 rpms and acts like it wants to die. Now, the SES light will come on going down the road then it will sometime cut off for a while. You see, vacuum and fuel circuit delivery problem seem to have the same symptoms and I just so happen to have trouble codes being spit out at me for both of those situations. Could one be causing the other? And swartlkk I really appreciate your knowledge and help with this.

Not knowing the specifics about the alarm you have, it is very difficult to comment on how much of an impact it has on your problem. Will the truck start at all if you disconnect your alarm?

No, it just turns over. I plan on pulling out the glove box today to check and make sure the harness is plugged in correctly on the ECM. The front has benn wrecked before and maybe when they pulled all that apart the harness was not reconnected correctly. I am going to start there first. Both of the codes tell me that I need to check that connection.