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2002-2005 Range Rover MkIII / L322
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19 Posts
Discussion Starter · #1 ·
Just purchased 2005 RR L322 4.4L V8 with 81,000 miles - great forum that I have found invaluable so far addressing a few minor issues during first 1,000 miles of driving.
While recently checking condition of air filter element while air intake was removed from throttle body, I manually opened the throttle plate to see if the interior of the throttle body needed a clean- looked OK so reassembled everything and I started engine.

Check engine light illuminated while idling and then "Engine Failsafe Prog" activated - no pedal response, rough idle, failsafe message in instrument cluster.

Checked codes with RSW All Comms and "P1639 Throttle adaption, spring test failed. Last occurrence - maximum signal".

Cleared P1639 code as well as the codes related to the triggering of failsafe mode and same routine upon restart.

Cleared codes again and disconnected MAF sensor - engine started and runs OK with no failsafe mode triggered but check engine light on with (not surprisingly) "P0103 Air mass sensor fault Last occurrence - maximum signal".

Checked all vacuum hoses (including PCV and hoses which were recently replaced by previous owner) and found the smaller of the 2 hoses that connect to the air intake pipe below the throttle body had split (probably during disassembly to check air filter) causing vacuum leak. Replaced small hose and rechecked all other vacuum hoses and wiring/connections but P1639 returns along with failsafe mode.

Next troubleshooting step was to clear all codes and then just turn on the ignition key to position 2 without starting engine and turn off. This triggered P1639 code.

From this I concluded the "P1639 Throttle adaption, spring test failed" was likely the source of the problem and that code is being triggered during the "pre-flight test" of the throttle body which initiates the failsafe mode.

I have removed the throttle body and checked the resistance across the integral potentiometers (following a procedure I found detailed on bimmer E39 forum) and found the following:

Throttle closed: Pot 1 696 ohms and Pot 2 1287 ohms
Throttle open: Pot 1 1423 ohms and Pot 2 395 ohms

The procedure suggested that the resistances should be the reverse of one another with throttle closed/open (within a few percent).

I'm pretty certain at this point that the throttle body has failed (due to me opening it manually??) but would welcome input from the forum members on their thoughts or ideas for further diagnostics/troubleshooting.
 

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Registered
2002-2005 Range Rover MkIII / L322
Joined
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19 Posts
Discussion Starter · #2 ·
Update to others that may have this problem: fitted new throttle body and all is well again. Leading theory on route cause was one of the potentioneters in the throlle body was bad and throttle was passing plausibity test by comparing good pot to maf sensor data. Vaccum leak threw off maf sensor calcs and then plausibility check relied on 2 throttle body pots and bad maf data which were all out of criteria and failed kicking in engine failsafe mode. It ran OK with maf disconnected because plausibility check was interrupted due to disconnection of maf.......sounds good anyway! A few hundred dollars lighter but engine running sweet again.
 
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