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95 STS P0300 after studding block


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Towards the end of summer I installed a stud kit from Norhtstar performance on my 99 STS. After that I had a p0300 code and a rough idle. You can actually feel the car rocking slightly back and forth at idle. Everything was good besides that. It had good heat and didn't overheat at all. Now it's ridiculously cold here in MI and I get no heat out of it. The engine temp goes to about the middle of the gauge where it should be but only blows cold air. This obviously is unacceptable. What should I check?? Any help or thoughts are greatly appreciated.

Edited by mcampau
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First you need to check for codes

Then check for vacuum leaks or disconnected vacuum hoses under the hood on the passenger side, there is a vacuum hose that controls the HVAC door functions.

Check your parking brake to see if it releases when you take the car out of park and tell us yes or no

A p0300 is an unspecified misfire. A misfire can be caused by many things including vacuum leaks, clogged injectors, plugs, ignition wires, coils, etc

Who did the head gasket job? Are the ignition wires routed correctly?

Check and post your codes and look for disconnected vacuum hoses

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

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I pulled codes and got a laundry list of Pcm codes

P0135 - Heated Oxygen Sensor (HO2S) Heater Performance Bank 1 Sensor 1

P0147 - Heated Oxygen Sensor (HO2S) Heater Performance Bank 1 Sensor 3

P0205 - Injector 5 Control Circuit CURRENT

P0300 - Engine Misfire Detected CURRENT

P0741 - TCC System Stuck Off

P1381 - Misfire Detected - No Communication with Brake Control Module

P1520 - Transmission Range Switch Circuit

P1527 - Transmission Range to Pressure Switch Correlation

P1602 - Knock Sensor (KS) Module Performance

P1604 - Loss of IPC Serial Data

P1611 - Loss of CVRTD Serial Data

P1612 - Loss of IPM Serial Data

P1613 - Loss of DIM Serial Data

P1614 - Loss of RIM Serial Data

P1615 - Loss of VTD Serial Data

P1626 - Theft Deterrent Fuel Enable Signal Not Received

All except the p0205 and the p0300 were history. After I pulled them I shut the car off and pulled them again just to double check and the only one that showed up was the P0205. That confused me a bit.

I have to head out in a little bit to get more kerosene for my heater because there's no way im spending that much time in 10° weather hunting this problem down! I will check the vacuum connections then.

On the parking brake question, do you mean the emergency brake? This car is supposed to disengage the e brake by itself when you put it into park? I have one rear caliper that is frozen right now so I dont want to mess with the e brake and have it be stuck on.

I did the head gasket work myself. The spark plug wires are routed correctly. I have heard about the problems that can cause so I made sure to diagram the routing before I took it apart.

So when I go back out in a little bit I need to check

1. Vacuum hoses in general, and specifically on the pass side connecting to firewall

2 ???

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All I can say is OH MY god.

No wonder you are having a misfire, the vacuum hose and heat are the least of your problem

You need to go back over all connections, grounds, etc . Check the connector at the ABS unit also its tricky

There is a vacuum hose connected to a T on the passenger side, it goes through the firewall and down toward the front bumper under the light where it should connect to a black vacuum storage tank. Make sure that is connected and holding vacuum

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I did the head gasket job. Im guessing a lot of those codes are because the car has sat for a few months in the cold and the battery died. The car runs, shifts and drives fine. The only issues are with the idle charactistics and the fact it pretty much has no heat if the amibient temperature is below around 35°.

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I did the head gasket job. Im guessing a lot of those codes are because the car has sat for a few months in the cold and the battery died. The car runs, shifts and drives fine. The only issues are with the idle charactistics and the fact it pretty much has no heat if the amibient temperature is below around 35°.

Ok do this, feel the heater hoses to see if they are warm going in and out of the heater core

You may need to flush your heater core

Your thermostat COULD be stuck OPEN, we have seen that happen, there are actually stats out there that fail OPEN...

What is your operating temperature?

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Since you said the car has sat and maybe the battery got low, try disconnecting your battery to get rid of the codes and see what comes back

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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After pulling the laundry list of codes the first time I shut it off then pulled them again and it was only the p0205 and p0300, both current. There were no history codes. This model doesn't show the actual temperature (that I've noticed) but during the summer the gauge gets to right about 12 o'clock and had great heat. Now in the winter after a long time it will reach about 11 o'clock on the gauge and not put out any noticeable heat.

Edited by mcampau
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So it sounds like you are running cooler if its at 11 oclock....

I would have a look at the stat, to see if its stuck open or to make sure its there at all, could it have been removed before the HG job? Read the temp number on the stat to make sure that no one put a low temp stat in

The injector code no doubt is the source of your misfire, check the connector, and the injector resistance

Feel the heater hoses, since there are no AC codes showing problems with your temp or door actuators, but your engine seems to be running very cool

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Check your parking brake to see if it releases when you take the car out of park and tell us yes or no

Check and post your codes and look for disconnected vacuum hoses

Mike, If I am not mistaken, the '99 went to an electrical (solenoid) parking brake release.

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Check your parking brake to see if it releases when you take the car out of park and tell us yes or no

Check and post your codes and look for disconnected vacuum hoses

Mike, If I am not mistaken, the '99 went to an electrical (solenoid) parking brake release.

OH, I just looked back it is a 99, he has 95 on his profile and only saw that......

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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So it sounds like you are running cooler if its at 11 oclock....

I would have a look at the stat, to see if its stuck open or to make sure its there at all, could it have been removed before the HG job? Read the temp number on the stat to make sure that no one put a low temp stat in

The injector code no doubt is the source of your misfire, check the connector, and the injector resistance

Feel the heater hoses, since there are no AC codes showing problems with your temp or door actuators, but your engine seems to be running very cool

I got the P0205 injector problem taken care of. Somehow the injector wiring was not fully engaged when it was plugged in. That made a tiny bit of difference with the idle quality but it is still really bad. Also the P0300 random misfire code is still current.

After quite a long run time the engine finally got up to proper temp (12 o'clock on the temp gauge) and both heater core hoses were definately hot. With the control set at 90° (max) it was blowing out luke warm air, no where near hot. If I rev the engine up to about 3k rpms the heat coming out does get hotter but no where near what I think it should be.

I hunted around for the vacuum line that you said should be on the passenger side that has a T in it and goes to a vacuum reservoir but couldnt find it. I went as far as removing the radiator shroud/cover and the pass. side light housing and saw no reservoir of any kind. Are you sure that it's supposed to be there?

Any other thoughts??

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I am confused now, the title states 95 and you refer to a 99 in the text here

What are you working on a 95 or 99?

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I got the P0205 injector problem taken care of. Somehow the injector wiring was not fully engaged when it was plugged in. That made a tiny bit of difference with the idle quality but it is still really bad. Also the P0300 random misfire code is still current.

After quite a long run time the engine finally got up to proper temp (12 o'clock on the temp gauge) and both heater core hoses were definately hot. With the control set at 90° (max) it was blowing out luke warm air, no where near hot. If I rev the engine up to about 3k rpms the heat coming out does get hotter but no where near what I think it should be.

I hunted around for the vacuum line that you said should be on the passenger side that has a T in it and goes to a vacuum reservoir but couldnt find it. I went as far as removing the radiator shroud/cover and the pass. side light housing and saw no reservoir of any kind. Are you sure that it's supposed to be there?

Any other thoughts??

Ok, because its a 99 much of what i said previously is wrong. They went from a vacuum brake release to a electric solenoid as Ranger notes. I also believe that the HVAC controller is different, whereas the controller was previously vacuum based.

But it sounds like your air control is working correctly as you are getting air out of the vents but your problem is that its not hot enough. I do not believe you are getting any AC codes that show temp or door actuator problems. BUT, if you are getting NETWORK codes, your AC system could be impacted. Check your codes again

What I would do if I were you would be to first check that your coolant level is normal, then remove the hoses from the heater core, not the core end but the other ends of the hose, reverse flush the heater core till it runs clean. Here is a photo of the cooling system flow. You can see that the coolant enters the core from the bottom and comes out the top, so you want to blow water into the TOP to reverse flush the core. Given the age of your car, the cores tend to clog up and flushing them restores their efficiency.

NSCoolingSystemCircuit.jpg

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Today I finally was able to pick up all the stuff I needed to flush the heater core. Now I'm just waiting for the engine to cool down enough to do that. While driving yesterday the service engine soon light came on. The only code was P0135 - heated oxygen sensor bank 1 sensor 1. Hmmmm???

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Reset it and see if it comes back, if it comes back you may need to replace it.

I had an O2 sensor code come up about a month ago on my 01 Monte Carlo, it has not come back

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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