What Does P1086 Mean?
The tumble generator valve position sensor on the left bank is reporting a voltage signal that is abnormally low. The ECM cannot accurately determine valve position for optimizing air tumble in the combustion chamber.
Common Causes
40%
Faulty tumble generator valve position sensor
30%
Short to ground in sensor wiring or connector
15%
Mechanical binding or damage to tumble valve preventing movement
10%
Poor ground connection or corroded sensor connector
5%
ECM internal circuit failure
Diagnostic Steps
1
Step 1: Inspect tumble valve position sensor connector for corrosion or damage
2
Step 2: Test sensor voltage at connector with key on, engine off (should be ~0.5-4.5V)
3
Step 3: Check wiring harness for shorts to ground using multimeter
4
Step 4: Verify proper 5V reference voltage supply to sensor
5
Step 5: Manually operate tumble valve and monitor sensor voltage change
Estimated Repair Cost
$200 - $600
Parts + labor, varies by vehicle and location
The tumble generator valve position sensor on the left bank is reporting a voltage signal that is abnormally low. The ECM cannot accurately determine valve position for optimizing air tumble in the combustion chamber.
The most common cause of P1086 (Tumble generator valve #2 (LH) position sensor circuit low input) is: Faulty tumble generator valve position sensor
Typical repair costs for P1086 range from $200 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is safe to drive. May experience slight reduction in low-end torque and increased emissions at certain RPM ranges.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1086 to identify the root cause.
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Quick Info
Category
Powertrain
System
Air Intake and Emissions Control
Difficulty
Type
Manufacturer
Recommended Tools
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