Mechanics

S, M, AND DRIVE LIGHTS ARE FLASHING - CHECK ENGINE LIGHT IS ON - NO POWER - SHIFT HANDLE LIGHT NOT ON

2004 Land Rover Discovery 2 • 60 miles

Reading code P0709, Intermittent transmission mode sensor circuit
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Edasse
October 3, 2011.



The park/neutral position (PNP) switch includes a transmission range switch.
The transmission range switch detects the selector lever position when the shift lever is in the N or P shift position and sends a signal to the Transmission Control Module

Possible causes

- Open or short park/neutral position switch circuit
- Poor park/neutral position switch circuit connection
- Misadjusted park/neutral position switch
- Park/neutral position switch may be faulty

BMRFIXIT
Oct 4, 2011.
These causes are included in the description of the code. We have seen both P0709 and P0705 which are very similar.

These symptoms, the S, M, and D flashing and the check engine light all occurred immediately after the installation of a new battery. They did not occur while the old battery was failing. When the new battery was installed, the terminal clamps were cleaned with a baking soda solution. The S, M, and D flashing started immediately, but, did not necessarily occur immediately after starting the engine, but was often delayed until the car had been driven for a while.

The day after the battery installation, the key could not be removed from the column. Several forums associate both these symptoms with battery problems.

I checked out the battery, alternator and starter and they checked out fine with the Auto Zone test system. I verified that the voltage at the alternator was the same as the voltage at the battery terminals.

The coincidence with the battery installation makes me doubt that the transmission range sensor is bad or that the harness and connectors are bad, but I can't identify the cause.

The dealership quotes the sensor at $800, so I am hoping to avoid replacing it.

I'm going to check out the fuses, but I can't think of anything that would initiate the problem with the replacement of the battery.

Can you suggest any places to look that might be dropping the voltage to the engine and transmission controllers?

Tiny
Edasse
Oct 5, 2011.
The problem did turn out to be the gear shift selector switch. It was merely a coincidence that it occurred when the battery was changed. The problem was caused by the AC condensate drain tube being located directly above the switch. Rather than pay $800 for a new one at the dealer, I was able to drill out the rivets, clean out the corrosion, moisture and dirt, apply some new silicone grease and fix the problem.

Fifty cents worth of rubber hose to divert the water around the switch would have avoided this problem; dumb design!

Tiny
Edasse
Oct 8, 2011.
What a coincidence, we had a disco in to day with the same problem, I remembered this post and went looking for it and you have just saved me a heap of diagnostic time, well I hope so, as we are pulling it apart in the morning to check if the switch has the same issue, here's hoping.

Mhpautos
Oct 13, 2011.