# P0172 - System too rich (Bank 1) Check Engine Light - '01 VW Jetta 1.8t GLS



## tran0262 (Jul 6, 2007)

Hello everyone,
I am having a problem with my 2001 1.8t Jetta GLS. Occasionally, I will get a check engine light while highway driving. The first time it happened, I was on an Interstate backed up in traffic going 10 feet and stopping and on and on for quite a few miles. I thought the constant stop-and-go traffic was what caused the error. I cleared the code, and didn't see anything while driving the car all week. Today, exactly a week later), I drove about 30 miles down the highway. This time, I was pulling out at a red light and noticed the check engine light coming on. Just two nights ago, I made the same exact trip down the highway as was made today, and there was no check-engine light. Therefore, the light isn't coming on as soon as it is cleared, but something is definitely wrong. I also notice some hesitation in some gears, regardless of whether or not the check engine light is on. I especially notice the hesitation while accelerating in 2nd gear. Again today, I cleared the code, revved the engine a few variation of ways (red-line rev, constant low-RPM rev, etc) and cannot reproduce the check engine light. I am expecting the check engine light to come back on in the very near future. Where exactly should I start to correct the problem, and how much should I expect to spend. I'm hoping this problem isn't going to be an expensive one. So far, I believe the #1 ignition coil has been replaced, and the MAF has been replaced as well. 
Thanks a lot everyone and please try to help in any was possible. Thank you.


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## veedubbinn (Jan 25, 2009)

*Re: P0172 - System too rich (Bank 1) Check Engine Light - '01 VW Jetta 1.8t GLS (tran0262)*

check dirty air filter, make sure the plugs are not fouled. do a tune up and see how it feels, if it still is not right then do further dianostics


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## tran0262 (Jul 6, 2007)

*Re: P0172 - System too rich (veedubbinn)*

Thanks for the quick response. I am planning on changing the Fuel Filter and the air filter on Monday. I will also schedule something with my mechanic to check for vacuum leaks and check all of the plugs / ignition coils. I will repost regardless of whether or not the problem is solved or not. Any other ideas as to what specifically it can be from personal experience ?


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## waabaah (Jun 24, 2006)

*Re: P0172 - System too rich (tran0262)*

Trouble code P0172 (VW 16556) Fuel Trim Bank 1 Rich. 
Tests/Procedures: 1. Check and verify that the fuel pressure is 36 PSI at idle, with vacuum to the fuel pressure regulator (44 PSI with no vacuum). Be sure that there is no fuel leakage into the vacuum line and that the vacuum line is intact and not leaking. 
2. Remove and replace the vacuum line to the fuel pressure regulator a number of times while observing fuel pressure. Make sure it changes between 36 and 44 PSI (approximate values) and does not stick high or low. Sticking indicates a faulty regulator. 
3. Check the N80 canister control valve, located on the passenger side of the engine compartment near the coolant reservoir, for leaking or sticking. The valve should not leak when de-energized. 
4. Using a full function factory compatible scan tool, observe data in the engine address word 01, function 08 read data blocks, display group 033 field 2 actual O2 sensor voltage. Verify that voltage fluctuates rapidly by at least 0.3 volts. Fixed voltages can indicate wiring harness or internal faults of the front O2 sensor. 
5. Check and verify that the engine oil is not fuel-fouled. Change it as necessary. 
6. Check and verify that the intake screens ahead of the air filter are clean and unobstructed. 
Potential Causes: Contaminated Engine Oil — Engine oil is fuel saturated.
Defective Fuel Pressure Regulator
Broken Fuel Pressure Regulator Vacuum Line
Restricted Intake Screens
Defective N80 Canister Control Valve
Defective Upstream Oxygen (O2) Sensor

Tech Tips: Most common failures: faulty vacuum lines to the fuel pressure regulator, sticking fuel pressure regulators or a sticking N80 canister control valve. Start diagnosis by checking these items first. 
Diagnostic Codes: 16556, P0172 
Author: Dave Tidaback 
Average Reported Mileage: 65000 

*AND*

Check Engine Light (CEL) is on. Trouble code P0172 (16556). 
Tests/Procedures: 1. Check and verify that there are no vacuum leaks or unmetered air leaks. 
2. Check and verify that fuel pressure is 36 PSI at idle with vacuum to the fuel pressure regulator. 
3. Check the Mass Airflow (MAF) sensor grams/second readings as follows: 
A. Idle (about 830 RPM) 3.5 grams/sec or more (4 to 4.5 grams/sec preferred). 
B. 2500 RPM no load, 9 to 15 grams/sec (11 to 12 grams/sec preferred). 
C. Wide Open Throttle (WOT) road load (drive vehicle at 45 MPH in 3rd gear and perform a WOT acceleration, observe maximum indicated grams/sec readings on the MAF). 90 or more grams/sec is preferred. 
A MAF that exhibits consistently lower than normal grams/sec readings can cause multiple misfire codes to set under a loaded engine condition. 
Potential Causes: Incorrect Fuel Pressure
Leaking Intake Air
Defective Mass Air Flow (MAF) Sensor
Leaking Vacuum

Diagnostic Codes: 16556, P0172 
Author: Steve Griff 
Average Reported Mileage: 92000 

*common problems are MAF sensor, O2 sensor, vacuum leaks, fuel psi regulator, N80 vavle *


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