What does it mean?
P0706 means that the Transmission Control Module (TCM) [or Powertrain Control Module (PCM), a combined engine and transmission controller used in many vehicles] sensed a “bad” signal from the Transmission Range Sensor (TRS). To explain, let’s first look at the automatic transmission shift linkage.
Typically, moving the shift lever through the various positions (P, R, N, D, 2, 1, etc.) moves a cable, which in turn rotates a lever (often called the manual control lever, or simply the manual lever) on the transmission. The TRS is an electro-mechanical sensor (mounted on or connected to the manual lever shaft) that tells the TCM which position (P, R, N, D, etc.) the transmission itself is in.
If the shifter cable breaks, or the linkage is misadjusted, the transmission could be in a position that doesn’t match the shift lever inside the vehicle, so it is important for the TCM to know the actual transmission position, not just the shift lever position. The TRS is often mounted outside the transmission (bolted to the case, with the manual lever shaft sticking through it), although in some transmissions it is mounted internally.
Typically, there are four or five signal wires running between the TRS and the TCM. There may also be additional wires (for the backup lights circuit, neutral safety switch, etc.), but P0706 only relates to a problem with the TRS position signal. The TCM senses whether each of the TRS signal wires is grounded or not. Within the TRS, the signal wires are either grounded (connected electrically to the metal transmission case, also referred to as “closed”) or not grounded (referred to as “open”).
The TRS gives a different combination of open / grounded signal wires for each of the transmission range positions (P, R, N, D, etc.), and also (usually) for the transition zones in between these positions. Therefore, the TCM can determine the transmission position by comparing the actual “code” from the signal wires (Grounded-Open-Open-Grounded, for example) to the proper code for each position.
There are two types of “bad” signals which can cause a P0706 fault: An “invalid” code: The TCM senses a TRS combination that does not match ANY valid position. An “illogical” code: The TCM senses a valid code, but in an unusual or illogical fashion.
Examples would be a TRS signal that changes instantly from “Park” to “1” (without any of the intermediate positions being sensed), or a “transition zone” code that persists for several seconds (as if the shift lever is being held in between two positions). So P0706 means that the TCM sensed an “invalid” or “illogical” TRS position code, for a certain length of time.