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My mom has a 2002 Discovery that won't pass emissions, but it runs normally otherwise.It was taken to the dealer, and they found a P0171 & P0174 code. They replaced the MAF sensor. They said they weren't able to drive it long enough for the ECM to recognize the drive cycle? I'm not sure what that means? I'm pretty handy with a wrench, but I'm unfamiliar with Land Rovers. Where should I start. Any help would be appreciated.
 

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You may need to drive it a couple of hundred miles for it to clear out the old codes. If you take it to the emissions folks before that the codes will still show. It just needs that to cycle back to ground zero.
 

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Fault codes stored in EEPROM can be cleared only with tester, if they were cleared and keep coming back it means the fault which triggered them is still present and must be eliminated to det rid of the codes, the ECU's memory(fault code log) is not affected by driving no matter how much... the driving thing is for the addaptive strategy, those codes are pointing more to a inlet or exhaust leak eventually low fuel pressure
 

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Intake manifold leaks are not uncommon, nor are upper plenum leaks. There are a bunch of vacuum points that could have leaking fittings or lines, and if it has SAI, that adds to the plumbing. At the age of this truck, these are pretty much expected issues.

A good independent shop can smoke test it and find it quickly. When you said "dealer" did you take it to a Land Rover dealership's service department?


While you are under there, you should also be looking at your cooling system plumbing. The expansion tanks are known to become brittle and burst, as is the vent tee. The TB heater's all leak and the plastic transfer lines get brittle. That and like all rubber parts, the hoses get soft. These trucks are highly allergic to any sort of overheat situation.
 

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On my Lexus when I failed emissions, I had to get it repaired and then drive a couple hundred miles so that it could cycle back to zero - then back to the emissions guys. Is it different for the LR or is it just that his specific codes do not reset that way when the repair is made?
 

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First off where are you located and what type of emissions testing is performed in your area?

Most common testing testing these days is an onboard diagnostics test ( plugging into the diagnostic connector).

If this is the case, the vehicle will require driving time through manufacturer prescribed "drive cycles " to reset all readiness monitors. After the vehicle has been through the its "drive cycles" it should have run its internal test procedures related to emissions self tests.
Performing drive cycles is not a Land Rover specific thing - every vehicle with O.B.D. 2 diagnostic protocol uses these procedures.
Once codes are cleared with an appropriate diagnostic scan tool they are GONE / erased from memory but the computer /engine management systems need to self test (required drive cycles).

From your information (limited detail) we could assume either it is fixed or ????? Not yet fixed. Have the codes come back? Engine light back on?
I have been an emissions inspector and certified repair technician for about 18 years dealing with both onboard diagnostic testing and also tailpipe emissions testing programs.
 

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Red - so essentially my advice to drive a couple hundred miles to reset and then go back to the emissions guys was correct?
Assuming that the fault is corrected and the codes do not re occur ...... Yes needs more driving time.
 

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Fault codes stored in EEPROM can be cleared only with tester, if they were cleared and keep coming back it means the fault which triggered them is still present and must be eliminated to det rid of the codes, the ECU's memory(fault code log) is not affected by driving no matter how much... the driving thing is for the addaptive strategy, those codes are pointing more to a inlet or exhaust leak eventually low fuel pressure
Not to split hairs but not exactly factual.
PROM = programable read only memory

E.c.u. Fault code memory /fault code log iserasable and after an erase the ONLYthing that can confirm the fix is drive cycles to allow for readiness monitors to reset after they have completed these self tests. Yes of course there are adaptive strategies /compensations for altitude and numerous other variables.

I will agree with you Sierra and also CT that it is more likely either an intake leak / vacuum leak, injector o ring, damaged or loose air inlet duct etc.
but have been going on the assumption that the truck was fixed by the dealer that serviced it and the codes are gone
 

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One would have to assume that they reset the ECU and deleted the active fault code when they did the MAF repair. And throwing a MAF at a D2 is a sure-fire indication that whoever was working on it didn't know what they were doing. It's usually something else.
 
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