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Juan Crespo
Juan Crespo, Tech Trainer
Category: GMC
Satisfied Customers: 1513
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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I have a question regarding a 2002 GMC Envoy SLT. The Mode 6

Customer Question

I have a question regarding a 2002 GMC Envoy SLT. The Mode 6 diagnostics is showing test fail in ALL areas of Weak Vacuum Test Fail 1 and 2. I have noticed a drop in performance and MPG which drove me to run the test
Submitted: 7 months ago.
Category: GMC
Customer: replied 7 months ago.
VIN: 1GKDT13S822430088
Make:GMC / Pontiac Year:2002• EVAP canister loading test
⚠ Status: Test not complete
TID:02 ID:04 Min:- Val:- Max:-• EVAP excess vacuum pass test 2
❌ Status: Complete and Fail
TID:02 ID:06 Min:0x803C Val:0x8000 Max:-• EVAP weak vacuum pass test 1
❌ Status: Complete and Fail
TID:02 ID:50 Min:0x80AF Val:0x7FB5 Max:-• EVAP weak vacuum test 2 vacuum
❌ Status: Complete and Fail
TID:02 ID:30 Min:0x13E Val:0x00 Max:-• EVAP weak vacuum test 2 vapor
❌ Status: Complete and Fail
TID:02 ID:40 Min:0xFFFF Val:0x00 Max:-
Customer: replied 7 months ago.
This could be unrelated, but I also have a MIL code as well, here are the live data recorded at the time of the code:PID : Description : Value04 : Calculated Engine Load Value : 100.0 %05 : Engine Coolant Temperature : 100 °C, 212 °F06 : Short Term Fuel Trim Bank 1 : 0.0 %07 : Long Term Fuel Trim Bank 1 : 5.5 %0B : Intake Manifold Absolute Pressure : 37.0 kPa, 10.9 inHg0C : Engine RPM : 2934 rpm0D : Vehicle Speed : 113 km/h, 70 MPHThe Check engine light is no longer on though
Customer: replied 7 months ago.
Here is an excel sheet showing the live data at Idle...
Expert:  Juan Crespo replied 7 months ago.
Hi there.Looks like you forgot to post the most important piece of information; the code number. Once we know what that is, then we'll be able to help you.
Customer: replied 7 months ago.
Hey Juan, so the code is P0495. Is related to my fan clutch I think. Not sure if it is revelent to the EVAP issues. Sorry for not including
Expert:  Juan Crespo replied 7 months ago.
OK. P0495 sets when the cooling fan RPM is too high when the PCM is commanding 0%, which usually mean the fan clutch is bad.I don't see how that code would prevent the EVAP monitor from completing since all that does is check the EVAP system for leaks and purge flow. What I do see is the EVAP canister loading test did not complete, which will make all the other EVAP test results irrelevant.I recommend you carefully drive that Envoy through a GM OBD-II Drive Cycle executing all driving maneuvers exactly as indicated so all the monitors have a chance to run and complete. Click here for that Drive Cycle.Best Regards.
Customer: replied 7 months ago.
I will that next. Can the high fan speed be related to a relay as opposed to the clutch. I just reached 100,000, so I assume the clutch. But if I can test the clutch I might be able to see if it needs to be replaced. Do you know a good way to test it? The problem is it's not a constant problem, it only has issues once in a while. I can here the clutch turn on/off. So I think the clutch is showing decay. But it doesn't explain the decrease in performance and MPG.
Customer: replied 7 months ago.
I should also mention, I am getting a U1000 code as well. I think it could be the onstar. I disconnect and reconnected it when I replaced the radio, but I used a non-compatible wiring interface. Happy to hear your opinion on this.
Expert:  Juan Crespo replied 7 months ago.
The P0495 code indicates the clutch was turning when the PCM was commanding it not to - it does that when the vehicle is cruising and the road air is sufficient to keep the engine at the desired temperature. Based on that, I don't see how the relay would be faulty. However, if you wish to test it, your best tools would be a Tech-II or equivalent scan tool and a scope. You see, this is a smart relay that sends a Pulse Width Modulation (PWM) signal (12-14 volts) to the cooling fan by the cooling fan clutch supply voltage circuit.Regarding the communications code, when a module does not associate an identification number with at least one critical parameter within 5 seconds of beginning serial data communication, DTC U1000 or U1255 DTC is set. When more than one critical parameter does not have an identification number associated with it, the DTC will only be reported once. All of which means that it is probably the OnStar causing this code.Best Regards.