P0706 on 2008-2014 Subaru Impreza: Transmission Range Sensor Causes and Fixes

What's Unique About the 2008-2014 Subaru Impreza

The 2008-2014 Impreza spans two generations with different automatic transmissions: a 4-speed automatic (4EAT) for 2008-2011 and a Lineartronic CVT (TR580) for 2012-2014. Despite this change, both transmissions commonly use the same externally-mounted inhibitor switch (Part No. 31918AA090), which is a known failure point. The most distinctive symptom on these Subarus is a flashing 'AT OIL TEMP' light, which often appears before or alongside the Check Engine Light for this code.

Generation note: This range covers the third generation (2008-2011, GE/GH) and the fourth generation (2012-2014, GJ/GP). The third generation used a 4-speed automatic transmission (4EAT), while the fourth generation introduced a Lineartronic CVT (TR580). However, the primary cause and fix for P0706, a faulty inhibitor switch, are common to both transmission types.

Symptoms You May Notice

• Flashing 'AT OIL TEMP' light on the instrument cluster.
• Check Engine Light is on.
• Engine will not crank or start when the shifter is in Park.
• Engine may start when the shifter is in Neutral.
• Reverse lights do not turn on when in Reverse.
• Gear position indicator on the dashboard may be blank or incorrect.
• Transmission is stuck in one gear (limp mode).
• Harsh or delayed gear engagement.

Most Likely Causes

1. Faulty Inhibitor Switch (Transmission Range Sensor) 🔴 High Probability → Shop Transmission Park Inhibitor Switch The switch is mounted externally on the transmission case, where it is exposed to moisture, road salt, and debris, leading to internal corrosion and failure over time. Subaru has even recalled newer models (2021-2023) for a similar switch failure due to water intrusion, indicating a historical vulnerability in this part's design and placement.
   How to confirm: A classic test is to see if the car starts in Neutral but not in Park. If so, the switch is almost certainly the culprit. A definitive diagnosis involves testing the switch's continuity for each gear position with a multimeter, following the factory service manual procedure.
   Typical fix: Replace the inhibitor switch. The new switch must be correctly aligned.
   Est. part cost: $65-$90
2. Misadjusted Inhibitor Switch 🟡 Medium Probability → Shop Transmission Park Inhibitor Switch
   How to confirm: Place the vehicle's shifter in Neutral. Visually inspect the alignment marks on the switch and its lever on the side of the transmission. If they do not line up, the switch is misadjusted.
   Typical fix: Loosen the switch mounting bolts and rotate it until the alignment marks line up. A 4mm or 5/32-inch drill bit can be used as an alignment pin to ensure accuracy. Tighten the bolts and re-check operation.
   Est. part cost: $0
3. Damaged Wiring or Connector ⚪ Low Probability
   How to confirm: Visually inspect the electrical connector and wiring harness leading to the inhibitor switch for any signs of corrosion (green or white powder), frayed wires, or physical damage. Pay close attention to the harness where it may rub against the chassis or exhaust components.
   Typical fix: Clean the connector terminals with an electrical contact cleaner or repair the damaged section of the wiring harness.
   Est. part cost: $10-$50

Rare But Worth Checking

• Faulty Park-Range Switch (in Shifter Assembly): On CVT models, a similar switch inside the center console shifter assembly can fail, often due to spilled liquids. This can cause issues with starting or key removal. This is less common than the main inhibitor switch failing but is a known issue documented in TSB 16-94-16R for the related Legacy model.
• Faulty Transmission Control Module (TCM): → Shop Transmission Assembly This is extremely rare and should only be considered after the inhibitor switch, its adjustment, and its wiring have been definitively ruled out as the cause.

Diagnosis Steps

1. Scan the vehicle for all trouble codes. Confirm P0706 is present, likely accompanied by P0700.
2. Attempt to start the vehicle in both Park and Neutral. If it starts in Neutral but not Park, this strongly points to an inhibitor switch issue.
3. Check if the reverse lights illuminate when the shifter is placed in Reverse. If they don't, this is another symptom of a faulty switch.
4. Safely raise and support the vehicle. Locate the inhibitor switch on the passenger side of the transmission case for 4EAT, or on top for the CVT.
5. Inspect the switch's wiring and connector for any visible damage, corrosion, or loose connections.
6. Check the switch alignment. Place the shifter in Neutral and verify that the alignment marks on the switch and lever line up. A 4mm or 5/32-inch drill bit can be used as a pin for this purpose.
7. If adjustment and wiring are not the issue, disconnect the switch and test for continuity across the pins for each gear position using a multimeter, following the factory service manual procedure.
8. If the switch fails the continuity test, it is faulty and must be replaced. If the switch and wiring test good, the fault may be with the TCM, which is very rare.

Parts You'll Likely Need

• Inhibitor Switch / Transmission Range Sensor (OEM #31918AA090) — This is the component that fails in the vast majority of P0706 cases on this vehicle. It is a widely used part across many Subaru models from this era.
  Trusted brands: Subaru (Genuine)
  OEM price range: $65-$90
  Aftermarket price range: $50-$75

Related Codes That Often Appear With This One

• P0700 — P0700 is a generic code that means the Transmission Control Module (TCM) has stored a fault. It is an informational code that almost always appears with a more specific transmission code like P0706.

Technical Service Bulletins (TSBs) & Recalls

• TSB 16-94-16R: While for a Legacy, it documents a related failure of the park-range switch within the shifter assembly, which can present similar symptoms and is relevant to CVT-equipped Imprezas.

Platform-Specific Known Issues

• While no specific recall exists for the 2008-2014 Impreza, Subaru has recalled newer models (2021-2023) for faulty inhibitor switches under recall WRQ-23 / NHTSA 23V-755. The cause was an insufficient weld allowing water intrusion, highlighting a long-standing vulnerability of this externally mounted part to the elements.
• A warranty extension for the CVT transmission was issued for some model years, but this program (detailed in bulletins like 16-115-18) covers internal failures and does not apply to the external inhibitor switch that causes code P0706.

Mechanic-Grade Diagnostic Values

• Inhibitor Switch Continuity Test (4EAT) — expected: With the switch disconnected, continuity should exist ONLY between the specified pins for each gear. Park: pins 4-3. Reverse: pins 4-2. Neutral: pins 4-1. Drive: pins 4-8. The starter circuit (for start/no-start diagnosis) should only have continuity between pins 12-11 when in Park or Neutral.. Failure: Continuity on incorrect pins for a given gear, or no continuity on the correct pins, indicates a failed switch.
• Inhibitor Switch Continuity Test (CVT TR580) — expected: Testing is performed at the black T3/B12 connector on top of the bellhousing. The pinout combinations for each gear position are defined in the service manual.. Failure: Incorrect continuity readings when shifting through the gears indicate a faulty switch.
• Inhibitor Switch Securing Bolt Torque — expected: 3.4 N·m (2.5 ft-lb).. Failure: Over-tightening can crack the switch housing; under-tightening can allow it to lose alignment.

Scan Tool Commands That Help

• Subaru Select Monitor (SSM) or equivalent professional scan tool: Live Data: Transmission Range Sensor Parameter — Use this to monitor the gear position being reported by the inhibitor switch to the TCM in real-time. As you move the shifter through P, R, N, D, the scan tool should display the corresponding position. Glitches, delays, or incorrect readings confirm a fault in the switch or its circuit.
• Subaru Select Monitor (SSM) or equivalent professional scan tool: Clear Memory / Clear DTCs — After replacing or adjusting the inhibitor switch, this function must be used to erase the stored P0706 and P0700 fault codes from the TCM's memory. This is a required final step before test driving to confirm the repair is successful.

Wiring & Ground Locations

• Inhibitor Switch Connector (B31) — On CVT models, this is the black connector (T3/B12) on top of the transmission bellhousing. On 4EAT models, it connects directly to the switch on the passenger side of the transmission case.. This is the primary connector to inspect for corrosion and to perform electrical tests (continuity, voltage) on the switch and its harness without having to access the TCM directly.
• Main Transmission Ground — A ground strap typically runs from the transmission bell housing to the firewall or chassis, often near the starter motor.. A poor or corroded main transmission ground can cause a host of erratic electrical issues, including unstable sensor readings. While not usually the sole cause of P0706, a bad ground can create electrical noise that interferes with the inhibitor switch signal, complicating diagnosis. Ensuring this ground is clean and tight is a fundamental step.
• Engine Ground (Intake Manifold) — Ground wires are bolted directly to the intake manifold, which serve as a primary ground point for the ECU and its sensors.. The ECU/TCM relies on a stable ground reference. A poor ground at the intake manifold can cause voltage offsets across the entire engine management system, potentially leading to false sensor codes like P0706. This is a known issue on Subarus.

Real Owner Repair Stories

• Subaru Legacy International forum user (Subaru with 4EAT transmission) — No reverse lights.
  ❌ Tried (didn't work) Initial diagnosis was uncertain.
  ✅ What actually fixed it The user was advised that the inhibitor switch was the most likely cause. The fix was to replace the inhibitor switch. A key piece of advice given was to use a pin in the alignment hole with the shifter in Neutral when tightening the mounting bolts to ensure correct adjustment.

OEM Part Supersession History

• 31918AA090 → N/A - Still current
  Heads up: While the part number 31918AA090 is used across many models and years, including the 2008-2023 Impreza, there is a different part number (31918AA101) for the CVT in the 2010-2014 Outback. It is critical to verify the part number for the specific transmission (4EAT vs. CVT) as they are not interchangeable.

Model Year Variations Within This Range

• 2008-2011 (4EAT Transmission): The inhibitor switch is located on the passenger side of the transmission case, where the shift lever attaches. The alignment procedure involves inserting a 4mm or 5/32-inch pin through the switch body and lever.
• 2012-2014 (CVT TR580 Transmission): The inhibitor switch is located on top of the transmission, and its wiring runs to a black connector (T3/B12) on the bellhousing. Electrical testing is most easily done at this connector.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Head Gasket Failure (EJ253 Engine) 🔴 High — Common on 2008-2011 non-turbo 2.5L models, typically between 100,000 and 150,000 miles. The issue is an external oil or coolant leak.
• Excessive Oil Consumption (FB20 Engine) 🟠 Medium — Affects early 2012-2014 models with the 2.0L FB20 engine. Caused by faulty piston rings, leading to oil burning between changes. A class-action lawsuit led to a warranty extension for this issue. (Ref: Subaru Technical Service Bulletin for piston ring replacement.)
• Premature Wheel Bearing Failure 🟠 Medium — Common across many Subaru models of this era, including the Impreza. Owners report a roaring or humming noise that increases with speed, often starting around 60,000-100,000 miles. Failure can be accelerated by road salt and moisture.
• CVT Torque Converter Lock-Up Clutch Issue 🟠 Medium — While more documented on Legacy/Outback models with the TR580/TR690 CVT, it can affect 2012-2014 Imprezas. Symptoms include stalling or very low RPM when coming to a stop, feeling like a manual car without the clutch depressed. (Ref: TSB 16-90-13R (and subsequent revisions) for a countermeasure torque converter.)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: A used inhibitor switch is generally not recommended. The part fails due to internal corrosion from exposure to the elements. A used part from a junkyard carries a high risk of having the same internal wear or corrosion, or failing shortly after installation. The low cost of a new OEM or quality aftermarket part makes it the smarter choice.

Donor-vehicle mileage cap: roughly under 50000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• If you must buy used, source it from a low-mileage vehicle from a dry, salt-free climate.
• Inspect the electrical connector pins for any signs of green or white corrosion.
• Ensure the plastic housing is not cracked or brittle.
• Verify the alignment holes are clean and not damaged.

OEM-only on this vehicle (don't cheap out):

• Inhibitor Switch / Transmission Range Sensor

Brands owners have reported issues with on this vehicle:

• Generic, unbranded parts from online marketplaces. Forum discussions frequently show these failing prematurely or having incorrect internal resistances, causing the code to return.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0700 — A general transmission control system malfunction code that frequently accompanies P0706 to trigger the Check Engine Light.
• P0705 — Transmission Range Sensor Circuit malfunction; closely related to P0706 as both involve the inhibitor switch's ability to communicate gear position.

Frequently Asked Questions