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My problem p0440 and p0172 - Computers & Internet

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HI. You have placed the Auto DTC codes in the wrong position under PC Desktops. With that said; I will provide the definitions to the DTC codes you have posted above and their respective causes and solutions.

P0440- Evaporative Emission System

This indicates that a part of the EVAP control system is no longer functioning correctly. The EVAP system consists of many parts, including the gas cap, fuel lines, carbon canister, purge valve, and other hoses. The (EVAP) emission control system prevents the escape of fuel vapors from a vehicle's fuel system. Fuel vapors are routed by hoses to a charcoal canister for storage. Later, when the engine is running a purge control valve opens allowing intake vacuum to siphon the fuel vapors into the engine. EVAP emission canister purge is controlled by a valve which allows engine vacuum to pull stored fuel vapors from fuel tank into the engine to be burned, rather than be vented into the environment. A vacuum switch is used to detect when flow exists. If the PCM/ECM commands purge and detects that the switch is closed, The code P0440 is set.

The most likely causes for this code will be a bad vacuum switch, broken EVAP line or canister, Restricted EVAP solenoid or canister, failed purge vale(likely culprit) or a failed PCM. A bad purge vale connector could also cause a misreading, as well. I would advise to reset the code and see if it returns. if so, check all the points above to correct. Replace any failed component that makes up the EVAP assembly.

P0172 - System Too Rich Bank 1

Basically this means that an oxygen sensor in bank 1 detected a rich condition(not enough O2 in the exhaust mix). This code will concern cylinder #1. The necessary actions are to:

  • Inspect all vacuum and PCV hoses, replace if necessary
  • Clean the MAF sensor. Consult your repair manual for it's location if you need help. We find it's best to take it off and spray it with electronics cleaner or carburetor cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
  • Inspect fuel lines for cracks, leaks, or pinches
  • Check the fuel pressure at the fuel rail
  • Check the fuel injectors, they may be dirty. Use fuel injector cleaner or get them professionally cleaned/replaced.
  • Check for an exhaust leak before the first oxygen sensor (this is unlikely to cause the problem, but it is possible)

  • NOTE_ Additionally; Concerning the P0440 code above, I would first remove and reinstall the gas cap, clear the code, and drive for a day and see if the codes come back. If it does, inspect all the points that I stated above in the P0440 code section. It would be a great idea to have a professional emissions tech to use a smoke machine to detect any leaks before you start your inspection.

Posted on Aug 23, 2010

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It is my husbands 1996 850 turbo SW, I had bought a Grupon oil change and maintenance inspection. He tested it and two codes p0172 and p0440, whatever that means. I don't drive the car, but I know it...

This is a combination of safety and environmental issues.


Driving with a damaged axle rubber boot will cause excessive wear on the CV axle. I will not recommend drive the car for extend period of time.

The axle grease will splatter on the inner wheel well and the ground your car travel to.


P0172 is a lean fuel mixture code

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In some case it's just a loose fuel cap.
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Axle $400+

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Find a good local independently own shop,the owner may able to combine all these job and give you a better price.

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I have a '96 Jetta, and i got P0440, P0302, P0172 and P1613 codes. How can I fix this? I have to go to emissions test this month, but my check endine light comes on because of these problems.

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Something unspecified is wrong with the evaporative emission system. Check vac lines. Could be a loose electrical connection. This code has a very vague description.

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Has the car had a tune up in the past few years? Check plugs and wires, test for spark. Maybe a compression test. This issue may cause the next code.

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I would clear up the misfire first, then this code might go away.

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Check the wiring under & behind the dash and instrument cluster. There apparently is a wiring issue, or the dash itself is shorted

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