Does your car say "Reduced Engine Power"? P2135 means your throttle sensors are fighting each other. Learn how to graph the "A" vs "B" signals wirelessly to find the liar.
1. What Does P2135 Mean?
The code P2135 stands for "Throttle/Pedal Position Sensor/Switch 'A' / 'B' Voltage Correlation."
On modern Drive-by-Wire cars (especially GM, Chevy, and Nissan), the Throttle Body has TWO sensors (Sensor A and Sensor B) built into it. This is a safety redundancy feature.
⚠️ Safety Shutdown
The ECU reads both sensors constantly. If Sensor A says the throttle is 20% open, but Sensor B says it's 50% open, the ECU panics. It doesn't know which sensor is telling the truth, so it triggers P2135 and forces the car into Limp Mode (P2104).
2. The "Argument" Between Sensors
Think of the two sensors like a Pilot and Co-Pilot landing a plane.
- Normal Operation: Both pilots agree on the altitude.
- Correlation Fault (P2135): The Pilot shouts "We are at 1,000 feet!" but the Co-Pilot shouts "No, we are at 500 feet!"
Because the ECU cannot verify which sensor is broken, it disables the throttle control completely to prevent the car from accelerating unintentionally.
3. Why Do the Sensors Disagree?
The Throttle Position Sensor (TPS) is essentially a potentiometer (like a volume knob) with a wiper sliding across a resistive track.
- Worn Tracks (Dead Spots): Over thousands of miles, the "volume knob" wears out in the spot you use most (cruising speed). This creates a "dead spot" where the signal momentarily drops to zero.
- Loose Wiring: The connector at the throttle body vibrates constantly. This causes "fretting corrosion" on the pins, leading to momentary signal loss.
- Water Intrusion: Water entering the sensor connector can bridge the 5V reference wire to the signal wire, skewing the data.
4. Diagnosis: Wireless Dual-Graphing
You cannot diagnose P2135 with a multimeter because the "glitch" happens too fast. You need to see the two sensor waves overlapping. The iCarsoft CR MAX BT (Bluetooth) allows you to merge these graphs wirelessly.
Step 1: Setup the Graph
- Plug in the VCI. Take the 7-inch tablet to the car.
- Turn Ignition ON (Engine OFF).
- Go to Live Data and select:
- TP Sensor 1 Voltage
- TP Sensor 2 Voltage
- Merge Graph: Combine them. (Note: On GM cars, Sensor 1 usually goes Up 0-5V, while Sensor 2 goes Down 5-0V. They should look like an 'X').
Step 2: The "Wiggle" & "Sweep" Test
-
Sweep: Slowly press the gas pedal from 0% to 100% and back.
- Good: Both lines move smoothly without jagged spikes.
- Bad: One line suddenly spikes down or up while the other stays smooth. That is your bad sensor!
- Wiggle: While someone watches the tablet, wiggle the throttle body connector wire. If the graph spikes violently, you have a bad wiring pigtail (very common on Chevy trucks).
See the Glitch Instantly
The iCarsoft CR MAX BT is the ultimate tool for "Correlation" codes. Its large 7-inch touchscreen allows you to overlay sensor graphs and spot the disagreement wirelessly, saving you from guessing which part is broken.
- Multi-Graphing: Compare Sensor A vs Sensor B.
- Wireless Bluetooth: Perform wiggle tests from under the hood.
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Throttle Relearn: Reset the idle after replacing the part.
6. Frequently Asked Questions
Q: Is it the Throttle Body or the Gas Pedal?
A: P2135 usually refers to the Throttle Body (on the engine). If the code was P2138, that usually refers to the Accelerator Pedal Position (APP) sensor (under your foot). However, always verify your specific car's manual.
Q: Can I just replace the sensor?
A: On older cars, yes. On most modern cars (2010+), the sensors are riveted into the Throttle Body assembly. You usually have to replace the entire Throttle Body unit.
Q: Do I need to reprogram the ECU?
A: Not usually, but you DO need to perform an Idle Relearn (Throttle Body Adaptation) after installing the new part. The CR MAX BT has this function built-in.
