GMC sierra question

It sounds like that:

The Coolant Temperature Sensor went bad. It is shorted on the cold side, and feeds too much fuel, because it's sending the computer a signal that the engine is very cold, in the summer weather we are having, and also when it's somewhat warm on restarts.

Hence, the low idle, rumbling and most likely some black smoke, diminished fuel mileage and a gas smell.

I hope this helps?

Refinish King

Hello Refinish

I was getting a fuel smell before this problem developed, so it is entirely possible that you are right. Would this show up on a diagnostic test when my mechanic puts the computer on it? He is going to do it this week sometime depending on his schedule.

I haven't noticed black smoke, or noticed diminished gas mileage, but I haven't checked the mileage lately.

Good ideas, I will suggest it to my mechanic, as he is baffled right now.

Thank you, Joe

It will show up on a scan:

It will never go to operating temperature and go into closed loop.

I hope this helps?

Refinish King

I am not sure what you mean by never go to operating temperature. My temperature gauge reads close to 210, which it always has once it is warmed up. I was wondering, if it is telling the computer that the engine is cold, then wouldn't the engine overheat eventually?

Joe

Not if the gauge is reading from another sensor:

Plus, with the mistake I made on that other advice I gave, to someone else. You might want to shoot me!

But I think your truck has a separate gauge sensor and CTS, and the computer always gets a cold signal from the CTS, and the computer never goes into closed loop.

The scan tool has a temperature reading in it, which reads the CTS.

I hope this helps?

Refinish King

By scan tool, do you mean the thingy the mechanic is going to plug in under the dashboard to diagnose the problem? BTW, where is the coolant temp sensor located under the hood? Is there a place on the web somewhere that shows where all the sensors are located on the 2000 GMC truck 4.8L engines? I have something of a background in electronics and if it is a thermistor, and I could locate it, I could test it with my digital multimeter cold, and then compare it to the reading I get when it is warm, maybe?

Joe

message

It is the sensor located in or closest to the thermostat housing:

It is a thermistor, and I don't have my chart for the temperature to resistance values here.

It's a two wire plug, with very small pins, so don't bend them. A better way to do it is: The wire going in carries a 5 volt input signal, and the wire exiting at a cold start should be 0 volts.

As it warms, the voltage should climb, anyone in the group, with my screw ups lately, please tell this guy if I'm wrong?

The voltage on the wire to the ECM should increase in voltage as the engine warms.

I hope this helps?

Refinish King

. . =3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D

Joe =3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D snipped-for-privacy@mindyourbusiness.com (Refinish=A0King)

It is the sensor located in or closest to the thermostat housing:

It is a thermistor, and I don't have my chart for the temperature to resistance values here. It's a two wire plug, with very small pins, so don't bend them. A better way to do it is: The wire going in carries a 5 volt input signal, and the wire exiting at a cold start should be 0 volts. As it warms, the voltage should climb,

anyone in the group,

with my screw ups lately, please tell this guy if I'm wrong?

The voltage on the wire to the ECM should increase in voltage as the engine warms. I hope this helps?

Refinish King

=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D howdy King, So far, looks like you're advice is pretty much solid. The only thing you may be off on is that the system should go "closed loop" even with a bad CTS. A function of the O2 sensor, is to act as a switch for closed loop I believe. If i'm wrong.....we'll here bout it in short order. lol

any whoooo..... here's a site to reinforce yer advice.

Repair for CTS Address:

marsh

~:~

Joe ======= =======

snipped-for-privacy@mindyourbusiness.com (Refinish King)

It is the sensor located in or closest to the thermostat housing:

It is a thermistor, and I don't have my chart for the temperature to resistance values here. It's a two wire plug, with very small pins, so don't bend them. A better way to do it is: The wire going in carries a 5 volt input signal, and the wire exiting at a cold start should be 0 volts. As it warms, the voltage should climb,

anyone in the group,

with my screw ups lately, please tell this guy if I'm wrong?

The voltage on the wire to the ECM should increase in voltage as the engine warms. I hope this helps?

Refinish King

====== ====== howdy King, So far, looks like you're advice is pretty much solid. The only thing you may be off on is that the system should go "closed loop" even with a bad CTS. A function of the O2 sensor, is to act as a switch for closed loop I believe. If i'm wrong.....we'll here bout it in short order. lol

any whoooo..... here's a site to reinforce yer advice.

Repair for CTS Address:

marsh

~:~

Thank you, Gents,

He will be using the scanner on Monday. I went to the link marsh provided. My problem doesn't seem to be that drastic, but I will let you know what the mechanic finds on Monday. So marsh, if I understand you correctly, it COULD be the O2 sensor?

Thanks again for the info, Joe

Thanks Marsh!

The O2 actually sets closed loop before the CTS, but if the ECM doesn't see the CTS voltage in the pre plotted time.

The ECM goes into back up fuel. There are more than one levels of back up fuel on a GM ECM. There are algorithms set for: CTS, O2, Ignition module timing (Usually code 42) and excessively rich conditions.

It's just been overwork, lack of sleep and sleazy real-estate deals making me the crazier than normal person that I am. It's actually starting to cloud my judgment. Glad I got some sleep last night and today.

Thanks for the help Marsh!

Refinish King

PS If I could only get rid of this headache, and convince the governor to have an open day on real-estate agents, my smile would return!

Joe ======= =======

snipped-for-privacy@mindyourbusiness.com (Refinish King)

It is the sensor located in or closest to the thermostat housing:

It is a thermistor, and I don't have my chart for the temperature to resistance values here. It's a two wire plug, with very small pins, so don't bend them. A better way to do it is: The wire going in carries a 5 volt input signal, and the wire exiting at a cold start should be 0 volts. As it warms, the voltage should climb,

anyone in the group,

with my screw ups lately, please tell this guy if I'm wrong?

The voltage on the wire to the ECM should increase in voltage as the engine warms. I hope this helps?

Refinish King

====== ====== howdy King, So far, looks like you're advice is pretty much solid. The only thing you may be off on is that the system should go "closed loop" even with a bad CTS. A function of the O2 sensor, is to act as a switch for closed loop I believe. If i'm wrong.....we'll here bout it in short order. lol

any whoooo..... here's a site to reinforce yer advice.

Repair for CTS Address:

marsh

~:~

. . ======= ======= Aug 6, 2004, 8:56pm (CDT+5) From: snipped-for-privacy@nospamearthlink.net (Joe) put forth:

Thank you, Gents, He will be using the scanner on Monday. I went to the link marsh provided. My problem doesn't seem to be that drastic, but I will let you know what the mechanic finds on Monday.

So marsh, if I understand you correctly, it COULD be the O2 sensor?

Thanks again for the info, Joe ======== ======== Joe, No, i don't believe it could be the O2 sensor. This is based on the symptoms you've posted. The O2 doesn't come into play untill after it's heated up.

I vote with "The King". Check to be sure the signal is good on the CTS circuit first. An open or shorted signal here will make the computer think you're starting the truck down in Antartica. So....get the dude to put the scanner on the truck and pay good attention to all the data signals.

Hard start when cold only could relate to a number of variances on the engine....

drawing too much air.... not dumping enough fuel.... combustion timing....

so any number of sensors or worn mechanical components could cause the symptom. A couple of them could be carboned up and letting too much air flow into the system on cold start. A couple of them could be sluggish due to whatever reason. One or two of them could be failed making the computer adjust air,fuel,ignition timing, for a "sensed" climate and load condition that isn't actually occuring.

so ....who knows.

Wait and git the scan done, do a repost with what yer dude comes up with, and if the prob isn't fixed.......the guys in here will lead you through some "not to technical" checks you can do over the next couple of days that will narrow it down even more.

it's guess work bud.....pure and simple.

Without KNOWING what's good....it's hard to do anything other than guess....at what could be bad. A scanner plays a big part in eliminating a lot of guess work, just by being able to see what data is responding, and even more impotantly, what data WILL respond.

Basic computer diagnosis....1+1=2

good in + good out = bad part

change good to bad on either input or out put and the final result will be the component to stare at.

post the scanner results .... be sure the dude gives you codes if any are set. Clear the codes....drive the truck....watch the data....check for codes again.

If he don't fix it....the guys in here WILL!! (it jest may take some time on yer part)

let us know,

Marsh ~:~ =========== ===========

Thanks, Marsh. I will get as much info as I can from him tomorrow and let you know.

Joe

Hi Guys,

I took the truck to the mechanic this morning and he put a scanner on it. I asked him to check the temperature of the coolant temp sensor also, and he said it read 90C and was climbing to 91 degrees C (truck was running). My temperature gauge read close to 210 degrees F, so I guess that's close enough.

Then he found 2 codes which he has to look up. I copied them right off the LCD screen on the scanner:

'P0463 Fuel Level SNSR ckt sig High/open'

'P0430 Catalyst Efficiency Low Bank 2'

Just some background, my fuel gauge has been malfunctioning for the last

I looked a little closer at that diagram of location of sensors at the link Marsh provided me, but it looks like it is for a car, not a truck. Are the sensors in the same place?

Anyway, just to summarize the problem again: On Cold starts, it starts right away. Once it warms up, I have difficulty starting it. It is a GMC year

Thanks for any info,

Joe

I had similar starting problems with my 5.3 when the fuel pressure regulator went south. Something to check, anyway. H

That catalyst inefficiency is something to look at:

It sounds like the catalyst is getting more fuel on the right bank, than on the left. Quite possibly a leaking injector on the right bank and a CTS that's a bit low.

I don't have a Celsius to Fahrenheit conversion chart, and what's the mechanic reading in Celsius for anyway. He must have the scanner set to metric too I bet?

Refinish King

Hi King,

He pointed out to me 4 (yes, 4!) sensors on the exhaust system that it could be. He's not sure which one is bank 2. As far as the temperature goes, I did a quick calc in my head knowing that 212F=100C(where water boils) so, with the temp gauge between 200 and 210F, I figured 90C was reasonable. He brought over some literature this afternoon for me to read regarding the sensors. This is regarding the code P0430. I will print what the document says below:

"In order to maintain a reasonably low emission of Hydrocarbons (HC) , Carbon Monoxide (CO) and Oxides of Nitrogen (NOx), the engine control system uses a three way catalytic converter. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas. This reaction converts them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to Nitrogen. The PCM monitors this process using bank 2 Heated Oxygen Sensor (HO2S) 2 bank, bank 2 HO2S2, located in the exhaust stream past the three way catalytic converter, produces an output signal which indicates the oxygen storage capacity of the catalyst. This determines the catalyst's ability to convert exhaust emissions effectively. If the catalyst is functioning correctly, the bank 2 H2O2S2 signal will be far less active than that produced by bank 2 H2O2S1. This indicates that the threeway catalytic converters oxygen storage capacity is operating at a threshold considered acceptable."

The title of the above document is 2000 GMC Truck K 1500 P/U 4WD V8-291 4.8L VIN V SFI copyright 2003, ALLDATA 8.00

So that's where we are at right now. He's not sure which is the Bank 2 H2O2sensor that seems to be causing the P0430 code.

Joe

So what's the next step? He doesn't know which is bank 2, and neither do I. I priced the sensors at the local napa and they are about US $90 each, so I would rather not guess and end up replacing all 4. Does anyone know where bank 2 is?

Thanks, Joe

Bank #2 is the side with the #2 cylinder:

The right side to be exact, but the scanner should have been precise in telling if it was sensor 1 or two.

If it's sensor or catalyst related, the factory has a EPA obligation to fix it under: The Emissions Warranty, which was and I think still is 6 years or

This seems to me to be a rich condition, and most likely is being caused by a defective CTS, which you'll get a free one, if you bought it at a reputable parts store?

Also, maybe a leaking injector on the right bank?

I hope this helps?

Refinish King

message

Hi King,

Thanks for the reply. I had a few questions;

I have over 90,000 miles on it now.

CTS is coolant temp sensor, as I said in a previous post, it appeared to be working properly. It said the temp was around 90C and the temp gage read between 200 to 210F (water boils at 212F=100C). I have not bought a new CTS.

Possibly, but how would this relate to the catalyst efficiency? I can tell my mechanic, but, as above, I don't know what you mean by 'right' or 'left'. Facing the engine, or sitting in the truck? They are opposites. Can you describe it in terms of driver's side or passenger's side?

Thanks, Joe