You are here:

Cadillac Repair/1997 Jimmy/Blazer PCM TESTING


QUESTION: Hi, and thanks in advance for your time.  My question(s) are related to the PCM and Smog Testing.
Is it possible to have a faulty PCM but the vehicle still operate?
My issue is that my PCM was cleared of trouble codes and reset several months ago.  Now I need a smog check and the PCM says the readiness tests are incomplete so I can't get it done.  They've told me to drive 100 miles to reset it.  I don't drive much due to being disabled, but have driven well over 100 miles since the reset at least 6 months ago.  And in an effort to complete the readiness, I have gotten on the freeway and just driven for a half hour then turned around and come back.  So roughly 50 miles roundtrip and I did this twice.  Still no-go.  Is there any way of testing the PCM for faults that will keep me away from the dealership?  Again, I'm disabled, (i.e. very low income with no room for any additional expenses) but I have a pretty good understanding of stuff and most tools to do any job and no physical limitations.  I just can't afford to go buy a new (or even used) PCM and then pay the dealer to flash program it so I'm hoping you can help.  I really appreciate your time and sharing of your knowledge.  Thanks again.

ANSWER: Hello,

Trust me when I say, I am very familiar with being on a disability fixed income. My first question if you are looking to save money is why on earth would you take a 1997 vehicle to a dealer? What because they represent the manufacture and know more about the vehicle than anyone? That is a common response, however not from those who have been totally ripped of for thousands of dollars because of their incompetence!
Many techs who worked on 1997 vehicles are no longer at the dealer. The information they have for diagnostic is no better than a reputable service center with a Tech II or equivalent electronic diagnostic scanner.

You ask if the vehicle will run with a bad PCM, and the answer is yes and depends on what exact problem the PCM has.

My suggestion is this: Take the vehicle to autozone. Be wary of what they are telling you is wrong with the vehicle because they are out to sell parts and are not technicians. They should have a diagnostic scanner they can plug into the OBD II (On Board Diagnostics) port to determine what issues if any are wrong with the vehicle.

I do have a stipulation here however, I am not from California and I know that emissions are set up the same for 49 states (except California) where it is my understanding that emission standards are much stricter than federal requirements.

In all my years as being a very experienced GM tech, I have never seen a readiness check message for the PCM. I am not saying that that isn't the case, I have never seen such a message.

The code checking can be done at Autozone. Normally though, the yellow check engine, emissions or some other light will come on. With the light on, or even after I believe it is up to 150 starts, codes should be retained. Better yet, with your OBD II system, the diagnostic scanner should pin point exactly what your problem is, whether a sensor, the circuit, or a PCM.

If I may, another suggestion I would like to make and I realize you are on limited funds. Check with and see if the go back far enough to 1997, in which they offer a service manual. If so, buy it online. It's $30 and will save you a ton of money performing your wn repairs. All the information is in the manual as for diagnostics, how to locate any component as well as instructions on how to replace. Much of this a layman can do. As I said though, I do not know if they go back that far.

Please save your money and shy away from the dealer. Find a reputable service garage in your area in the event you can't repair this problem yourself. Going to autozone and the new diagnoses will also offer you confirmation on the problem

I wish you good luck!

[an error occurred while processing this directive]---------- FOLLOW-UP ----------

QUESTION: A little more info.....I have an OBD-II scan tool.  When I hook it up and press start, this is what I find;  a) Initial Scan Results : MIL Status = OFF / DTC Count = 0 / Readiness Complete = NO / Freeze Data Exists = NO........then it goes to the menu screen.  I scroll down to #5) I/M Status - then scroll thru the results.  All say "OK" or "N/A" with these exceptions;  Catalyst Monitor = Incomplete / Evap System Monitor = Incomplete / O2 Sensor Monitor = Incomplete / EGR System = Incomplete.  Leads me to think that 'part' of the PCM may be damaged.  However, there are no stored dtc's - hard or soft.  And regarding the 'stealership', I would normally never consider it.  But I worry about an independant trying to make more of it than it really is.  Now, I'm really in a fix.  Got a damn ticket being parked in front of my apt.  Tags are way past due. PAID, but no tag due to smog.  Only parking is on the street.  Tried to dispute it, got shot down.  Now they want $350 + smog + ALREADY sent to the state collections dept after two days!  Unheard of!  For the cherry on top?  They say they will buy the vehicle from me - BUT - ONLY after it FAILS smog.  Can't get it smogged to pass OR fail until PCM is ready.....have you ever been trapped in a vicious circle?  I think I'm in one.......
Thanks again for your time.  It seems like you may be able to provide me with more advise with this added information.  I look forward to it with great appreciation.


Actually I had a similar situation with an ex wife and the fine crap Wisconsin courts. Couldn't sell her though. No one wanted her, and yes, I fixed the problem nicely! I moved to Texas where I had no more income tax, no more corporate tax, and yes in a county that does not give a rats butt about emissions!
My Olds has so many lights n the dash, it is like a Christmas tree and still passes inspection even with the driver's side mirror missing!

As I have told you, I have had countless complaints here on dealers replacing perfectly good parts, charging for parts and labor and never fixing the problem.
I have 11 years with GM dealers and it would scare the Hell out of you if I started with the stories of my techs!

If you go to a reputable service center which will cost less than the dealer, it has been my experience having owned my own repair shop for 17 yeas, to get the job done right the first time, because you need that customer back.

I do not feel comfortable with a generic OBD II scan tool for diagnostics. A tech II (dealers use on GMs) is what should be used here and many service centers have them. The Tech to should pin point exactly what you need. Not all scan tools are equal.
For years, I used OTC scan tools and other makes, but I would end up with generic information like you appear to be getting. By the way, I appreciate you giving me more information on your problem.
What bothers me is that you have no hard or soft codes, which normally would be coming from the PCM if faulty. I just hate to see you change the PCM on a guess.

Why don't you call around to service garages and see who has a Tech II and how much to scan to confirm or deny your current testing. In the event it requires a PCM, generally you will see the scan fee waved from the garage if they change the part. I am not going to say if it is the PCM or not, but I would be expecting codes to go along with the scan tool and you don't have that. Look at all the things that are incomplete with the scan tool. In theory, if you had all that wrong and running in open loop which is what the scanner says, I would question how the engine is running!
At this point, am I correct that you really don't know if it will pass or fail other than what you are reading from this scanner? What prompted you to get the scanner? The PCM is not telling you of these problems, the scanner is.
After thinking about all this, I think you out either take it in and see if it passes or fails (might pass if your scanner s not accurate) or take it to a service garage with a tech II and don't say anything about the PCM. Tell them you want to make sure it will pass smog and see what they have to say. Don't tell the you scanned it.

Let me know what happens.

Cadillac Repair

All Answers

Answers by Expert:

Ask Experts


Rob Painter


Alarm system questions cannot be answered on this forum. These systems are not what I can answer. Without being physically at the vehicle and not knowing what kind of electrical service has been done on the vehicle, there is no possible way to give an accurate answer over the internet. My expertise is in Ignition/key based anti-theft systems. These issues include GM VATS (resistor chip in key blade) PASSLOCK (MRD)-ignition lock rotation based, no special ignition key and the PKIII Transponder (computer chip in key) systems. These systems are not alarm based and are integral with the starting of the engine. This is why I cannot diagnose alarm problems without physically looking at the vehicle: Alarm systems are a completely different annimal than ignition key/lock based anti-theft system. Many alarm questions come from vehicles 10 years old, and since older, many hands that had been involved over the years.I am an expert in all GM factory (ignition/key based)systems. Alarm system questions pose to many situations beyond my knowledge as to what has been done to the vehicle over the years. Some guy may have actually wired the stereo into the alarm system. Who knows? Over my past 30 years in vehicle wiring repair, I have seen unbelievable wiring disaters done by guys that consider themselves "mechanics." I have seen stereos and alarms intalled using surgical tape. I have seen modules burn up, un-fused circuits, wiring jambed between the doors and even lamp cord used for a starter kill. To answer alarm questions over the internet without examining the vehicle is like asking; What does it take to remove a dent?


Education/Credentials-ASE certified. 11 years with a GM dealer and 17 years with a repair facility dealing with only the repair of theft recovered vehicles.

©2017 All rights reserved.

[an error occurred while processing this directive]