P2135: Throttle/Pedal Position Sensor/Switch 'A' / 'B' Voltage Correlation
Electronic Throttle Control (Drive-by-Wire) systems utilize two independent Throttle Position Sensors (TPS 1 and TPS 2) inside the throttle body. As the throttle butterfly opens from 0% to 100%, Sensor 1 voltage increases (0.5V to 4.5V) while Sensor 2 voltage decreases inversely (4.5V to 0.5V). At all times, the sum of TPS 1 + TPS 2 must equal approximately 5.0V. If the ECM detects a correlation discrepancy exceeding 0.20V for just 0.1 seconds, it immediately cuts throttle actuator power and enters protective 'Reduced Engine Power' limp mode.
Driveability & Safety Advisory
DANGER: Limp-Home Mode (Reduced Engine Power). The vehicle computer will drastically restrict throttle opening, limiting vehicle speed to 15–25 mph with no acceleration response. Driving on busy highways or intersections is extremely dangerous.
Official Manufacturer TSB Advisories
Factory Condition: Fretting corrosion and high resistance on throttle body harness connector terminal pins causes intermittent TPS voltage drops.
Factory Condition: Throttle body internal gear teeth wear or motor servo winding resistance fault causes correlation errors.
Physical Component Location & Service Access
The electronic throttle body is mounted to the front of the intake manifold. The Throttle Position Sensor is sealed inside the black plastic side cover of the throttle body.
Electrical Specifications & Live PID Benchmarks
Scan Tool Live Data Targets
Digital Multimeter (DMM) Specs
Documented Model-Specific Case Studies
Root Cause: Terminal fretting on throttle body wiring pigtail connector causes intermittent 0.3V drop.
Verified Fix: Cut off old pigtail connector; solder and heat-shrink updated gold-plated harness pigtail.
Technician Inspection & Testing Workflow
Turn Key ON Engine OFF. Connect scan tool and navigate to live data: graph TPS 1, TPS 2, and Absolute Throttle Position.
Slowly depress accelerator pedal from 0% to 100% over 10 seconds. Watch graph lines. If either line has a sudden dropout, spike, or flatline, the throttle body potentiometer is defective. Replace throttle body.
Inspect 6-pin connector: Check for backed-out terminal pins, green copper corrosion, or oil contamination.
Clean throttle body bore: If carbon is heavy, use throttle body cleaner on microfiber cloth (never spray directly onto motor shaft).
Perform Throttle Relearn procedure using scan tool after replacement.
Recommended Diagnostic Tools & Verified Parts
BlueDriver Bluetooth Pro OBDII Scan Tool
Wireless sensor telemetry & enhanced diagnostics (Engine, ABS, Airbag). Delivers verified vehicle repair reports.
Autel AutoLink AL519 / AL319 OBD2 Scanner
Color screen standalone scanner. One-click I/M emissions readiness status, freeze-frame data, live DTC reset.
AstroAI Digital Multimeter 6000 Counts TRMS
Auto-ranging multimeter for measuring sensor pin resistance (ohms), live DC bias voltage, and circuit continuity per OEM specs.
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Cost Breakdown
Tools & Parts Matrix
Diagnostic Questions & Answers
Can I just replace the TPS sensor instead of the whole throttle body?
On most modern vehicles (Ford, GM, Toyota, Honda), the TPS is permanently ultrasonic-welded inside the throttle body housing. Replacing the complete throttle body assembly is the only reliable factory-approved repair.
Why do I need to do an idle relearn after fixing P2135?
Because the ECM has adaptive memory calibrated to an old, dirty, worn throttle plate. Installing a new throttle body without resetting throttle adaptations causes high idle (1,500+ RPM) or surging.