Is this the Intake Gasket Issue?

[dre2kx]

Just picked up my first GMC ever (got the Denali). To test it out, I put about 300 miles on it to and from other cities. I noticed that after my initial 100 miles, the rear windows (on the barn doors) were sparkling. Checked it out and it appeared to be drops of clear fluid. Cleaned the windows assuming it was from road debris or something and put another 100+ miles and noticed the same thing all over again. Wife's windshield also picked up those sprinkles when driving behind me once. The amount of coolant in the reservoir remained about the same as much as I can see and the oil still looks great. Did not over heat (temp stayed just under the quarter mark on the low end the whole time). At mile 300+, the check engine light came on and AutoZone reports 2 oxy sensors and random misfire. This look like the typical symptoms of the manifold gasket? Thinking of tackling it in the garage this weekend.

 

[SunlitComet]

get the specific codes and get a misfire history of each cylinder for a period of one minute at idle and a minute during driving. perhaps you should check all your fluid levels and condition regardless to monitor them for leaks.

 

[dre2kx]

I'l check out all the fluids over the next few days to see where else it could possibly be. I'll post up the codes from AutoZone tonight. Is there a particular tool I'd need to buy to perform those checks on the misfire history?

 

[_Dylan_]

Check for coolant leaks on the back of the block on the passenger side. It usually drips onto the starter. Another way to check is the color on the inside of the oil cap. If it is orange/red then it is or was drinking dexcool.

But the big indicator is to just keep an eye on the coolant level in the radiator (not the reservoir). If it is loosing coolant that is the easiest way to know. By the time I changed mine, it would eat about a quart of water on the way to the grocery store and back. Luckily not much got in the oil though.

It is a pretty straight forward repair. How many miles are on it?

 

[dre2kx]

Never thought about the radiator. Adding that and the starter area check to tonight's list. This one's at 170k. I had a 97 tahoe that I got rid of back in 2009 with 330k and it was running just as smooth (still kicking myself for that) so figured 170 wasn't too bad.

 

[SunlitComet]

the reservoir can tell loss too. as for the misfire history you may have to go to a shop with a scanner good enough to do it. autozone probably sells one but is commonly not the one they use for free testing.

 

[dre2kx]

Did a complete lookover and saw that everything around the tailpipe was bone dry. Went a little further and looked over the entire undercarriage and saw it: transfer case is all shiny and dripping wet with the same clear oil. It's nice n heavy right where the rear shaft enters it. Sooo... pretty sure now that the leak and the engine light are two different things.
After researching the web it appears this is probably the rear shaft seal (about $8 at AutoZone).

Any ideas how much pain is involved in pulling the shaft and replacing the seal? I'm up for the challenge if it takes the weekend.

Also, could this have hurt the TC? I obviously have not run ALL the oil out yet...

 

[SunlitComet]

you just remove the four bolts holding on the the rear of shaft to rear axle and pull the whole thing out. then use a seal puller of some sort.

Now this oil may be an issue too. if you have an obs yukon denali then you have not just 4wd you have auto4wd. you control panel would say auto 4wd on it as well. the fluid uses in that system is different then the non-auto4wd. the fluid should be blue in color in a auto4wd system and not red or clear. you need two quarts of this. the part number is on the bottle.:

you will find the plugs here:

Drain what ever is in there, do your seal and reinstall everything. fill it up and run it thru its paces. if the leaks persists the bushing in the housing or yoke may be worn as well.

---------- Post added at 10:18 AM ---------- Previous post was at 10:15 AM ----------

Transfer Case Output Shaft Seal Replacement (Rear) Removal Procedure

1. Raise the vehicle. Refer to Vehicle Lifting.
2. If equipped, remove the transfer case shields.
3. Remove rear propeller shaft.
4. Remove the rear output shaft seal.

Installation Procedure

• Tools Required
• J 29162 Rear Output Shaft Seal Installer.

1. Install the seal.

1.1. Lubricate the seal mating surface with Automatic Transfer Case Oil GM P/N12378396. 1.2. Install the seal using the J 29162.

1. Install the rear propeller shaft.
2. Check the transfer case oil level and add oil as necessary.
3. If equipped, install the transfer case shields.
4. Lower the vehicle.

---------- Post added at 10:18 AM ---------- Previous post was at 10:18 AM ----------

oh and post that code as well.

 

[dre2kx]

Thanks! That's going to be a huge help for me getting this done. I'll check AutoZone for that special tool.

Here are those codes:
P0161
P0141
P0300

 

[SunlitComet]

Circuit Description
The Heated Oxygen Sensor (HO2S) is a sensor designed to create a voltage relative to the oxygen content in the engine exhaust stream. The Control Module (PCM/VCM) supplies the HO2S with signal High and Low circuits. Ignition voltage and ground is supplied to the HO2S heater by independent circuits. The oxygen content of the exhaust indicates when the engine is operating lean or rich. When the HO2S detects that the engine is operating rich, the signal voltage is high, and decreases the signal voltage as the engine runs leaner. This oscillation above and below the bias voltage, sometimes referred to as activity or switching, can be monitored with the HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm the sensor to operating temperature and maintain the operating temperature during extended idle conditions. The HO2S needs to be at a high temperature in order to produce a voltage. Once the HO2S has reached operating temperature, the Control Module monitors the HO2S bias, or reference, voltage as well as the HO2S signal voltage for closed loop fuel control. During normal Closed Loop fuel control operation, the Control Module will add fuel (enriches the mixture) when the HO2S detects a lean exhaust content and subtract fuel (leans-out the mixture) when the HO2S detects a rich exhaust condition.

Certain vehicle models utilize an oxygen sensor after the catalyst converter in order to monitor catalyst efficiency.

This DTC determines if the HO2S is functioning properly by checking for an adequate number of HO2S voltage transitions above and below the bias range of 300-600 mV. This DTC sets when the VCM fails to detect a minimum number of voltage transitions above and below the bias range during the test period. Possible causes of this DTC are listed below.

• An open or a short to voltage on either the HO2S signal or HO2S low circuits.
• A malfunctioning HO2S.
• A problem in the HO2S heater or its circuit.
• A poor HO2S ground.

This DTC determines if the post-converter HO2S heater circuit is functioning properly by monitoring the amount of time required for the HO2S to reach operating temperature. This DTC sets when the VCM fails to detect HO2S voltage transitions above and below the bias range within a specified amount of time. Possible cause of this DTC are listed below.

• An open circuit in either the HO2S ignition positive voltage or the HO2S heater ground circuits
• An HO2S heater element problem

Conditions for Running the DTC

Important: This test is void if the system voltage remains outside the specified range for more than 4 seconds

• The system voltage is between 11.7-18 volts
• The MAF is less than 35 g/s
• The engine run time is more than 2 seconds
• The ECT is less than 33°C (91°F)
• The IAT is less than 33°C (91°F)
• The difference between the ECT and IAT is 5°C (9°F) or less

Conditions for Setting the DTC
The HO2S sensor voltage remains within 150 mV of the start-up voltage for 245 seconds after cold start.

Action Taken When the DTC Sets

• The Control Module illuminates the Malfunction Indicator Lamp (MIL) if a failure is detected during 2 consecutive key cycles.
• The Control Module will set the DTC and records the operating conditions at the time the diagnostic fails. The Control Module stores the failure information in the scan tools Freeze Frame and/or the Failure Records.

Conditions for Clearing the MIL/DTC

• The Control Module turns OFF the MIL after 3 consecutive drive trips when the test has Run and Passed.
• A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the Engine Coolant Temperature is more than 70°C (158°F) during the same ignition cycle).
• Use the scan tool Clear Information function.

Diagnostic Aids
Check for the following:

An intermittent may be caused by any of the following conditions:

• A poor connection
• Rubbed through wire insulation
• A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis. See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Symptom Related Diagnostic Procedures

Test Description
The number(s) below refer to the step number(s) on the Diagnostic Table.

2. As the heater warms the oxygen sensor to operating temperature, the HO2S will output a voltage in relation to the amount of oxygen in the exhaust. With the ignition ON and the engine OFF the exhaust usually contains a high oxygen content. With the engine OFF the HO2S voltage will usually decrease from the initial: (bias) voltage due to the high oxygen content.

4. This step checks for proper HO2S heater ignition feed and ground supply.

5.This step checks for proper VCM and signal circuit operation.