Hey guys Im new to the site but I need some help with my 96 blazer
with 4.3 auto. intermittemtly the vehicle will start to buck ant the abs/brake light will come on and off when this happens it will also set codes for the tps voltage and the egr pintle. if you pull over and restart the vehicle all is fine until it happens again, have replaced tps sensor,iac,
and egr. im thinking possible pcm problem please help!!!!!!!

 

If the truck bucks badly enough it'll turn on the ABS light. Why don't you post the actual codes? Also is there any kind of a pattern when it acts up? Taking off from a stop? Flooring it to pass someone? When you're just cruising along at 55? Intermittent problems are the worst. Mine used to do that pulling onto the highway at full throttle but I had to do a data capture while it was acting up to find out it was the crank position sensor, never had a code. (and NO I'm not saying throw one of those at it!)

 

wish i still had the paper with the codes but i lost it, the code for the tps was tps
voltage too low, checked voltage to the sensor and checked the wires to the pcm
no apparent probplems. when the issue appears is is only under light throttle driving.
it almost acts like a vacuum leak when it happens thats why I replaced egr also it has a code for the egr pintle performance, have montored all sensor with drb and cant seem to get it to act up with the scanner on, damn thing will only do it when I have to be somewhere. but the egr,tps,and iac are brand new. I did notice the pcm has reman sticker on it wondering if the owner before me had a reman put in and that is the problem. please help!!!!

 

Reman PCM isn't any less reliable than a stock one, don't stare at that sticker too long. It very well might be the problem but there's a way to diagnose it and work your way to it. Did you have it rescanned after throwing those parts at it? Do it & get a new sheet. Makes it much easier to diagnose and look for a correlation. P0122 - TP Sensor Low Voltage for example, the second to last thing to try is replacing the sensor. Replacing the PCM is the last thing, when all else has failed. I don't know what "drb" is but do you have a scanner? If you can monitor sensors it would be easier to track.
The problem you have is a wiring problem, the 5v+ is rubbed through and shorting to ground, or it's broken somewhere, or a bad connection OR a different component connected to that 5v line is shorting and drawing it down. See where the other EXACT codes come in handy? What other sensor(s) do we need to investigate? do they wire up to this one somehow? (in the case of that particular code MAP, EGR, Fuel Tank Pressure)
Assuming I nailed that code number correctly and that one is on the list do this: with the key on, with a digital voltmeter; disconnect the TPS sensor and measure the voltage between the black and gray wires. Is it at least 4.7 volts?
This is NOT an approved testing method but..... You could also try disconnecting your MAP sensor, EGR valve, Tank Pressure Sensor, and TPS sensor (only disconnect 1 sensor at any time) and driving. It won't run well, but it'll be consistent. When it runs consistently and quits laying down with a sensor disconnected, that's the one shorting out intermittently - if it's a shorting sensor. Get the code list.

 

A failing ignition switch can cause these symptoms as well.

 

thanks for the advice guys. I cant get the codes to reset because the problem happens so quick it wont log the codes since I cleared them when I replaced the tps and egr valve. I have tried to duplicate it in the driveway by shaking the wiring harness and wiggle testing the connector plugs to the sensors with no reaction from the vehicle. but it still buck, it starts off very suttle uner light throttle, and will become more violent when the abs and brake light flash on but the check engine will not set a code yet. guess Ill keep driving until it does.also just wonering if there are any tell tale signs when looking at the ignition switch for failure, like hot spots or a certain burnt wire. on another note this vehicle is very very very clean belonged to a 72 year old man that kept it ina garage its whole life, it only has 57000 miles on it, and the guy took very good care of it.

 

The only way to know for sure that it is the ignition switch is to remove it and take it apart. Sadly, it is quite difficult to get back together properly. I have one on the bench that I have dissected with the thought to show everyone what can happen inside these switches.

 

well finally got it to act up again and set codes. here are the codes p0122 tp or app
sensor 1 crkt short/low, p1122 tp ckt intermittent low voltage, p1406 egr pintle position ckt problem. now I have replaced the egr valve, tps sensor and checked all
wiring to these sensors back to the pcm with no visible damage also have shook the entire wiring harness and connector plugs with no luck getting it to act up only while
driveing under light throttle. any help would be great.

 

Sounds like the 5V reference from the PCM is dropping out intermittently. Since these two sensors do not share the same 5V feed from the PCM, it is possible that it is a PCM problem.

First, I would inspect all of the grounds, especially those on the back of the driver and passenger side cylinder head.

Have you backprobed the connections and monitored the 5V reference and ground quality during operation?

 

I have tried to check 5 volt ref but again this proplem only seems to happen under load and cannot duplicate in the driveway no matter how hard I try. I was leaning toward a pcm as well simply for the fact that there was a reman pcm in the vehicle anyways. called the local GM dealer and my cost on a new pcm is $268.00 plus $95 to program,I am almost at the point to just try one if no more ideas