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Evaporate system leak test failed

Tiny
XJSHEN
  • MEMBER
  • 2003 PONTIAC MONTANA
  • 3.4L
  • V6
  • 2WD
  • AUTOMATIC
  • 85,000 MILES
Evaporate system leak test failed by code reader. While Got code p0172, and service engine soon light. Repair shop repaired p0300, but created p0172. What is possible reason from fix p0300 and that cause p0172?
The reason for p0300 was throttle body gasket was leaking, and now it was fixed, and no misfiring.
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Saturday, November 21st, 2020 AT 2:39 PM

15 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,747 POSTS
Hi,

The idea that you had a P0300 first could have caused the Po172 to set. That code indicates a rich fuel mixture. Basically, the engine is getting more fuel than it needs.

Since you had a misfire, that could have allowed unburned fuel to enter the exhaust and set this code. What I would do is this. Reset the computer (delete the code) and see if it comes back. If it does, then I would recommend checking to see if there is an issue with fuel pressure. There is a vacuum hose that attaches to the fuel pressure regulator they may have left disconnected. See pic 1 I circled where the vacuum hose will be connected.

The regulator is located on the fuel rail on the top of the engine. Check to make sure that hose is connected. If it is, disconnect it and make sure there is no fuel in it which would indicate the regulator is bad.

If you want to check fuel pressure, here is a link that shows in general how it is done. However, I would try what I suggest first.

__________________________________

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

tHE ATT
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Saturday, November 21st, 2020 AT 8:17 PM
Tiny
XJSHEN
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Thanks a lot for your instructions and help!
How to reset computer? If need a specific professional DTC reader to do "Reset the computer (delete the code)"? I do not have that only have Astron CP 9575. And it can erase code p0172, but if run faster than 50 MPH then create again same code. At low mileage under 35mph not create p0172.

1. I have checked fuel pressure and that was normal. The vacuum hose that attaches to the fuel pressure regulator was tight and okay. How to know if fuel pressure regulator was bad?
2. I checked MAF sensor and found the ground terminal and MAF sensor signal terminal. When battery voltage was 11.85V, MAF sensor signal and ground terminal voltage was 11.05V, after full charge battery with 12.48V, it was 11.30V. It was said the voltage should be 12V. I do not know why the voltage only at low level than standard. How to check its connectivity problem or some resistance, or fuse problem? If that was the problem causing p0172?

Thanks for your instruction and help!
Steven
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Saturday, November 28th, 2020 AT 4:20 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi Steve,

The fuel pressure regulator will either cause high fuel pressure or it can allow fuel to be drawn into the engine via the vacuum hose I mentioned. Did you disconnect the hose to see if it is dry?

We have a rich fuel mixture, so at this point, we need to get a scan tool that can read live data. I need to know two things. First, what are the short term fuel trims. Second, is the engine coolant temperature signal to the computer accurate?

Are you able to get your hands on a live data scan tool?

Let me know.
Joe
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Saturday, November 28th, 2020 AT 8:01 PM
Tiny
XJSHEN
  • MEMBER
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I looked at several different value on the Data stream:

Fuel system 1 status CL
Fuel system 2 status ---
calculated load value 3.9%
Engine Coolant Temperature 219F

1. Short Term Fuel Trim - Bank 1 -3.1% / Long Term Fuel Trim Bank 1 -25%; Intake Manifold Absolute 13.8 inHg; Engine RPM 639 /min

2. Short Term Fuel Trim - Bank 1 -2.3% / Long Term Fuel Trim Bank 1 -25%; Intake Manifold Absolute 13.8 inHg; Engine RPM 644 /min

3. Short Term Fuel Trim - Bank 1 0.8% / Long Term Fuel Trim Bank 1 -25%; Intake Manifold Absolute 13.2 inHg; engine RPM 705 /min

4. Short Term Fuel Trim - Bank 1 3.1% / Long Term Fuel Trim Bank 1 -25%; Intake Manifold Absolute 12.9 inHg; engine RPM 688/min

speed at neutral 0 RPM
ignition timing advance for #1 17.5 C
Intake air temperature 80 F
Air Flow Rate from Mass Air flow sensor 0.8/ ib/ min
absolute throttle position 0.0%
Oxygen sensor output voltage (0.755V B1-S1)
Short Term Fuel Trim (B1-S1) 3.1%
Oxygen Sensor Output Voltage (0.340V

Short Term Fuel Trim (B1-S1) 99.2%
OBD requirements OBD &OBD2
Distance Traveled with mile is 0 miles activated.

Thanks for your review and help!
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Thursday, December 3rd, 2020 AT 7:44 PM
Tiny
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I do not know your second question: is the engine coolant temperature signal to the computer accurate?
Because I do not have smart scanner to read its status and reset them.
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Thursday, December 3rd, 2020 AT 8:03 PM
Tiny
JACOBANDNICKOLAS
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Hi,

The fuel trims are within range. In a perfect world, they would be 0, but even an engine running perfectly will range between -10% and +10%.

The temperature indicates the engine is at operating temperature. Is that when it was checked? If so, check it when the engine is cold to see if it is close to ambient temperatures.

Let me know.
Joe
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Thursday, December 3rd, 2020 AT 8:16 PM
Tiny
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Now cleared p0172 by replacer MAF sensor, but could not clear EVAP system monitor INC though run several time for EVAP system monitor drive cycle. What is standard Board PID_VP value on montane? Now my car engine vacuum is 64Kpa and passed by general scanner streaming data. And pre-test conditions for the EVAP system monitor drive cycle is over 75Kpa. And temperature difference between ECT (33.0000F) and IAT (19.000F) was 14F. If this is problem? Thanks for your instruction and help!
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Sunday, December 13th, 2020 AT 7:30 AM
Tiny
XJSHEN
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Now cleared p0172 by replacer MAF sensor, but could not clear EVAP system monitor INC though run several time for EVAP system monitor drive cycle. What is standard Board PID_VP value on montana? Now my car engine vacuum is 64Kpa and passed by general scanner streaming data. And pre-test conditions for the EVAP system monitor drive cycle is over 75Kpa. And temperature diffence between ECT (33.0000F) and IAT (19.000F) was 14F. If this is problem? Thanks for your instruction and help!
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Sunday, December 13th, 2020 AT 7:35 AM
Tiny
JACOBANDNICKOLAS
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Hi,

As far as a drive cycle, I've had them take up to 200 miles. I'm not sure how many miles you have put on it at this point. The readings you are showing me don't see anything too far out of the ordinary.

As far as an evap leak, have you smoked the system?

Let me know.
Joe
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Monday, December 14th, 2020 AT 2:38 PM
Tiny
XJSHEN
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Yes. First time a Tepdon scanner gave wrong result, that made me wasted a lot of time. I made vacuum leak smoke detector, but there was no any leak. After following GM guided EVAP signal driving cycle operation protocol cleared the EVAP INC.
Thanks a lot for your persistence support and instruction that led me to fixed problem.
Again thanks!
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Tuesday, December 15th, 2020 AT 8:44 AM
Tiny
JACOBANDNICKOLAS
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Hi,

You are very welcome. I'm glad to hear you got it fixed. Please feel free to come back anytime in the future if you need help. You're always welcome.

Take care,
Joe
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Tuesday, December 15th, 2020 AT 5:52 PM
Tiny
XJSHEN
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IAT/ECT IAT/ECT
0.39819005 0.325791855

Now I/M Monitors on scanner showed: Since DTCs cleared: run 160 mile

Misfire Monitor OK,
Fuel system Mon: OK,
Comp Component: OK,
Catalyst Mon: OK,
EVAP System: Mon Inc
Oxygen sensor Mon: OK,
Oxygen sensor Htr: OK
EGR system Mon: OK

MIL status: found: 0; CodeMonitor OK: 7; Monitos Inc:1;
Freeze data: No
Memory test
INT RAM: passed
INT FLASH: Passed
EXT FLASH: 30%

IAT/ECT rage: 0.325791855 to 0.39819005
IAT (F) : 72F to 88F
ECT (F):

So, the †EVAP system Mon Inc status’ could not be activated. So, can not pass inspection. I already run two GM drive cycle, but could dot activate EVAP system Monitor.
Large Leak will set DTC P0455; Small leak will set for p0455; Canister bad will set DTC P0446, EVAP Purge Solenoid Valve Leak will set DTC P0496, Gas cap leak will set DCTs.
What will be the reason that could not activate the EVAO system sensor?
If the 'EVAP system Mon Inc' status is related to H2S, Heated Oxygen Sensor Bank 1? Sensor bad can cause this problem? Thanks for your review instruction!
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Sunday, January 17th, 2021 AT 2:26 PM
Tiny
XJSHEN
  • MEMBER
  • 218 POSTS
Here is data view:
Engine speed (RPM %) 699 667
Calc load (%) 3.1 3.1
MAF (LB/M) 0.65 0.67
MAP ("Hg) 13 12.4
Coolant (F) 221 221
IAT (F) 72 88
IGN ADV 0.0 19.5 17
ST FTRM 1 (%) 0 -3.9
LT FTRM (%) -9.4 -11.7
VEH speed (MPNH) 0 0
FUEL sys 1 clsd clsd
Fuel sys 2 n/a n/a
O2S11 (V) 0.658 0.75
ST FTRM 1 (%) -2.3 -3.1
O2S12 (V) STAT 0.795 0.755
Problem may be came from Long term tream value and short term tream value?
If these vale indicating that HO2S 1 sensor must be replaced?
Thanks for your help!
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Sunday, January 17th, 2021 AT 4:05 PM
Tiny
XJSHEN
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All were cleared. Just circuite connector problems that caused EVAP sys monitor Inactivation!
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Monday, January 18th, 2021 AT 11:46 AM
Tiny
JACOBANDNICKOLAS
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Hi,

Glad to hear you got it fixed. Please feel free to come back anytime in the future if you have questions or need help. You are always welcome here.

Take care,

Joe
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Monday, January 18th, 2021 AT 8:13 PM

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