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2002-2005 Range Rover MkIII / L322
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Discussion Starter · #1 ·
So here I am again with another automatic transmission error. I have a 2004 L322 4.4 petrol which has started throwing up an intermitent Trans Failsafe Error which also leaves a P0720 (Output Speed Sensor Circuit) fault code. Here is what has been happening. The problem does not always happen and I can go a couple of days with no errors while doing the same trip to and from work. When I do get the error there is a 'Bong' along with the trans failsafe error message on the dash but nothing happens to the gearbox and I am able to drive normally, around 10 secs later another 'Bong' and trans failsafe error message but still no change in the car then a third 'Bong' and trans failsafe error message another 10 secs later but this time the car goes into limp home mode and stays in 4th gear. I can clear the fault code successfully while still driving but the car remains in limp mode. If i turn the engine of for a few mins and start up again the fault has gone and the car drives noramlly again with all gears available. This morning I had a slightly different experience, I still got the 'Bong' Trans failsafe errors every 10 secs or so but this time I had a forth 'Bong' and trans failsafe error message but the car carried on driving with no problem all gears available. There were no more bongs and the car continued to drive normally. Also during the initial bongs and messages there are no fault codes it is only when the car goes into limp mode that the error code appears. I know the obvious thing is to change the output speed sensor but I thought I would see if anyone has had the same issue before I do anything.
 

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2002-2005 Range Rover MkIII / L322
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Discussion Starter · #2 · (Edited)
Update.

Driving home from work had the 'Bong' and Trans Failsafe message, then a second 'Bong' and Failsafe message but this time the car went into limp mode and 4th gear on the second bong. Stopped the car turned the engine of then back on again and all gears now available in normal mode. A few hundred metres down the road the exact same thing again with 2 bongs and into 4th gear and limp mode. Again restarted the engine and all OK with no issues. Arrived home a couple of miles later, checked for error codes and cleared the P0720 error code.
 

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2006-2009 Range Rover MkIII / L322
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37 Posts
So here I am again with another automatic transmission error. I have a 2004 L322 4.4 petrol which has started throwing up an intermitent Trans Failsafe Error which also leaves a P0720 (Output Speed Sensor Circuit) fault code. Here is what has been happening. The problem does not always happen and I can go a couple of days with no errors while doing the same trip to and from work. When I do get the error there is a 'Bong' along with the trans failsafe error message on the dash but nothing happens to the gearbox and I am able to drive normally, around 10 secs later another 'Bong' and trans failsafe error message but still no change in the car then a third 'Bong' and trans failsafe error message another 10 secs later but this time the car goes into limp home mode and stays in 4th gear. I can clear the fault code successfully while still driving but the car remains in limp mode. If i turn the engine of for a few mins and start up again the fault has gone and the car drives noramlly again with all gears available. This morning I had a slightly different experience, I still got the 'Bong' Trans failsafe errors every 10 secs or so but this time I had a forth 'Bong' and trans failsafe error message but the car carried on driving with no problem all gears available. There were no more bongs and the car continued to drive normally. Also during the initial bongs and messages there are no fault codes it is only when the car goes into limp mode that the error code appears. I know the obvious thing is to change the output speed sensor but I thought I would see if anyone has had the same issue before I do anything.
Before doing anything drastic you should check the condition of your battery. I experienced a similar condition until I replaced the battery installed by the PO that was at end of warranty at the time I bought the car a couple of months ago and undersized anyway. The MTP-49/H8 will not cut it. You need the MTX-49/H8. The former has 730 CCA while the latter has 900 CCA. This matters as on first start up the starter can pull the volts down, especially when we have the air compressor running, the Harmon Kardon cranking out Queen, A/C running, etc.

It would occur for me on first startup of the day or after sitting and cooling off so the automatic environmental systems would also be sucking volts running the fans. I used a plug in voltage meter in the cigarette lighter socket so I could compare the onboard diagnostic voltage display and could see differences at times. The diagnostics would show 11.5V while the socket displayed 12.0 - 13.8V. At that same time a direct reading with a calibrated Fluke DVM could show 13.8V across the battery terminals.

I read somewhere that the ECU provides the voltage threshold for the networked electronics but the diodes in the alternator voltage regulator can fail and give you erratic voltage to the ECU. Both high and low outputs are possible if any diodes fail. It's also possible that the TCU is being fed wrong voltage or just 'thinking' it's getting low voltage. Check all the battery connections, ground connections and plug connection in the E box.

After installing the new more powerful battery the condition has mostly gone away. But once everything os warmed up, say after 10-15 minutes driving it will remain okay all day. I'm about to flush the "sealed' transmission to see if clean fluid and a new filter might help too. The RR SC is around 95000 miles old and I believe it's recommended, unofficially, to service the transmission around 75000, so I'm late.
 

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2002-2005 Range Rover MkIII / L322
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Discussion Starter · #4 ·
Here is an update of what has been happening. I was reading on this forum about transfer box problems possibly causing other fault codes and decided to test the transfer box. I was able to select the low gear ratio and return to high ratio with no problem. I then decided to drive in low ratio which resulted in constant error bongs along with a message which was either 'Select Neutral or Transfer box Neutral' (I cant remember which it was). I didnt even get of the drive when this happened so I stopped and selected neutral but was unable to return to high ratio. Turned the car of and on but still stuck in low ratio. I managed to get back into high ratio using the fuse 37 fix. i tried again and the same proble with neutral messages but this time the fuse 37 fix didnt work and i was unable to get the car back into hi ratio. The only way i managed to get the car back into hi ratio was to remove the battery for 30 min and after replacing the battery I was able to shift back into hi ratio. I didnt try to select low ratio again but the strange thing is that this was last thursday and eversince i removed and replaced the battery i have not received a single error regarding the output speed sensor circuit and the gearbox has run absolutely fine. I am too scared to go anywhere near the hi/low ration swith for more testing especially while all seems to be working OK.
 

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Here is an update of what has been happening. I was reading on this forum about transfer box problems possibly causing other fault codes and decided to test the transfer box. I was able to select the low gear ratio and return to high ratio with no problem. I then decided to drive in low ratio which resulted in constant error bongs along with a message which was either 'Select Neutral or Transfer box Neutral' (I cant remember which it was). I didnt even get of the drive when this happened so I stopped and selected neutral but was unable to return to high ratio. Turned the car of and on but still stuck in low ratio. I managed to get back into high ratio using the fuse 37 fix. i tried again and the same proble with neutral messages but this time the fuse 37 fix didnt work and i was unable to get the car back into hi ratio. The only way i managed to get the car back into hi ratio was to remove the battery for 30 min and after replacing the battery I was able to shift back into hi ratio. I didnt try to select low ratio again but the strange thing is that this was last thursday and eversince i removed and replaced the battery i have not received a single error regarding the output speed sensor circuit and the gearbox has run absolutely fine. I am too scared to go anywhere near the hi/low ration swith for more testing especially while all seems to be working OK.
I have the identical issue: How can I find the part number for replacement for the 2004 4.4 HSE M62 Engine - TRANSFER CASE ACTUATOR MOTOR?
 
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