|Trouble Code||Fault Location||Probable Cause|
|P0706||Transmission range (TR) sensor/switch range/performance problem||Wiring, TR sensor/switch|
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What Does Code P0706 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.
What are the common causes of code P0706 ?
Intermittent (non-repeatable) electrical issues (such as startup in extreme cold)
TRS was disconnected while key was ON
TRS failed internally
Corrosion in TRS (or TCM, or inline) wiring connector
Misadjusted shift linkage (if P0706 was caused by an “illogical” TRS signal)
Bent terminal pin in TRS (or TCM, or inline) wiring connector
Terminal pushed out of TRS (or TCM, or inline) wiring connector
Broken TRS signal wire
TRS signal wire shorted to ground
TRS signal wire shorted to another wire in its harness
Metallic (or non-metallic) debris (for TRS that is internal to transmission with exposed contact points)
Bad TCM / PCM
What are the symptoms of code P0706 ?
In some cases, there are almost no symptoms. Some TCMs can determine the actual transmission range position by other means (monitoring pressure signals, for example), so they can continue to operate normally even with an invalid TRS code. In these cases, typically the only symptom is an unusual instrument cluster display (such as ALL of the transmission positions being indicated at the same time, or a blinking transmission range display).
In other cases, the Check Engine Light (also known as the Malfunction Indicator Light or MIL) may be illuminated, and the transmission may be in “limp-in” mode (stuck in one gear, or other limited operation). The exact symptoms vary depending on the specific transmission model in your vehicle.
How do you troubleshoot code P0706 ?
P0706 faults are often caused by a faulty TRS, or by a wiring problem (broken wire, poor connection, etc.) between the TRS and the TCM. In some cases, the “bad” TRS signal is only temporary, and the problem “heals itself” after a few seconds (I have personally seen this happen at startup in very cold temperatures). If the problem was only momentary, and doesn’t recur, you can probably just ignore it.
For a recurring P0706 fault, note the transmission range position(s) where the problem occurs. Then consult a repair manual or check online for information about the TRS (and its wiring) for your particular transmission model. Use this information to determine the most likely root cause. For example, if you keep setting P0706 in Reverse, and your research shows that TRS signal wire #2 should be grounded in Reverse (but open in the other positions), then a broken or corroded TRS #2 signal wire (that is not making a good connection to ground) would explain your particular problem. So you would focus first on that wire / circuit.
If you have access to a scan tool that can display the actual TRS signal readings, check whether the proper TRS signal is present at each shift lever position, and see how far you have to move the shift lever (in either direction) to get a “transition zone” code. In some transmissions, a misadjusted shift linkage can cause P0706, if (for example) a slight nudge on the shift lever (when in Drive) produces a continuous “Drive to Neutral” transition code. Make sure the TRS signal is stable (and correct) at each shift lever position, and remains good as you wiggle the lever slightly. The transition zone signals should be centered between the shift lever detents, not biased to one side or the other. Readjust the shift linkage if needed.
For the next steps, chock your wheels and apply the parking brake. Then disconnect the wiring harness for the TRS at the transmission (at the TRS itself, if the TRS is external). Check the harness connector, and the TRS / transmission connector, for any obvious problem, such as corrosion, a bent pin, or a terminal that is pushed partway out the back of the connector. Also check the connector at the TCM for similar issues. Check your vehicle wiring diagram to see if there are any inline connectors between the TRS and the TCM (if so, check those connectors for the same issues). If the wiring connections all look OK, use a multimeter to check the resistance from each of the signal wire terminals on the TRS to ground (the transmission case). Check the resistance in each gear range (PRND) as a helper moves the shift lever (with engine OFF!). See if there are any positions where one or more pins are grounded (when they shouldn’t be) or open (when they shouldn’t be). If you find a problem, you can simply replace an external TRS. If the TRS is inside the transmission, you might want to remove the transmission oil pan and valve body assembly, and inspect the TRS and surrounding area for debris, before replacing the TRS. Sometimes a metal chip can short out one of the contacts on an internal TRS (grounding that contact when it shouldn’t be), and the repair is as simple as removing the debris.
In some transmissions, the TRS must be adjusted (if it’s replaced) for proper alignment with the transmission shift mechanism, and performing that adjustment will likely require the use of a scan tool (to read the TRS signals). So be prepared to borrow a scan tool, or have a shop assist you. Your transmission / vehicle repair manual should explain whether any TRS adjustment is required.
If the wiring connections look good, and the TRS itself checks out OK, check the resistance of each of the TRS signal wires between the TRS and TCM. They should have no more than 0.5 ohms resistance. Next, check each of these signal wires for resistance to ground (with both ends of the harness disconnected). They should all show “open” (infinite resistance) to ground. Finally, check the resistance between the TRS signal wires (again, with both ends of the harness disconnected) and every other wire in the harness (to check for two wires that are shorted together). Repair or replace any wires where problems are found.
If everything checks OK, including the wire resistances, then you may have a faulty TCM. But before spending a lot of money to replace the TCM, you might want to try this: Swap two of the TRS signal wires, at BOTH ENDS of the harness. You can use a special tool to unlatch the individual wiring terminals from the harness connectors, and then slide the terminals out the back of the connector. Using such a tool (or having a shop help you), slide out two of the TRS signal wires (the SAME two wires!) at each end of the harness. Then SWAP the terminals and reinstall the wires into the “wrong” cavities in the connectors. Let’s say you swapped the #1 and #2 signal wires at each end of the harness. Now the wire that used to carry the #1 signal is carrying the #2 signal instead (and vice versa). Using our example above, suppose the #2 signal wire is the likely “culprit” (if you have a “suspect” wire, make sure it is one of the two that you swap). Now drive the car or simply exercise the shift lever, and see if the P0706 sets in the same manner as before (in Reverse, in our example). If so, then the wire is not the problem (since the wire that was #2 isn’t connected to the #2 circuit any more). In this case, you might now replace the TCM. If, however, P0706 now sets in some other transmission position(s) (corresponding to the #1 wire), that indicates that the wire is indeed the problem (and not the TCM).
Codes Related to P0706
Other manufacturer-specific TRS codes
If the problem is related to a more global voltage problem, you might see various Low Battery Voltage or TCM Input Voltage Low codes (such as P0562, P0882). In this case, diagnose and repair the low voltage codes first (that may also fix the P0706).
BAT Team Discussions for P0706
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