OBD codes / P2138
P2138
SeriousThrottle/Pedal Position Sensor D/E Voltage Correlation
Take P2138 seriously: the computer has lost trust in the pedal, and many cars will sharply limit power or drop to idle without warning. It's usually possible to limp to a nearby shop, but don't rely on the car for highway driving or traffic that demands quick acceleration until it's fixed.
What this code means
The two accelerator pedal sensors (D and E) must always agree about where your foot is — they run on different voltage scales, but their relationship is fixed. P2138 sets when their voltages stop correlating: the computer sees two conflicting stories about pedal position and can no longer trust either. Unlike the 'circuit low' codes (P2122/P2127) where one signal is clearly dead, a correlation fault often means both signals are alive but drifting apart — classic signs of a worn sensor track inside the pedal assembly, or of a poor connection adding resistance to one signal. Because an untrusted pedal is a genuine safety issue, most cars respond with firm reduced-power or even idle-only operation. The pedal assembly is the most common fix, but corroded connector pins, chafed wiring, and (rarely) water intrusion into the harness can cause the same disagreement for far less money.
Symptoms you might notice
- Reduced-power or 'limp' mode, sometimes idle-only
- Pedal that responds erratically or cuts out under way
- Surging or hesitation, especially at steady throttle
- Symptoms that appear intermittently, often when hot or over bumps
- Check-engine light, often with a throttle/ETC warning
What it costs to fix
Typical range: $40–$450 · about ~0.3–1 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Connector / wiring repair | $5–$100 | ~0.3–1 hrs |
| Accelerator pedal assembly | $80–$300 | ~0.3–1 hrs |
The pedal assembly is the usual fix and it's a quick under-dash job, so total cost stays moderate. A scan-tool check of both sensor traces first is worth it — a smooth-but-offset pair suggests wiring/connector, while a glitchy dropout in one trace points at the pedal.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P2138 for my exact vehicle →
How to fix P2138
Moderate — doable at home with common tools and patience
- Inspect the pedal connector under the dash
Unplug the accelerator pedal connector and examine the pins for corrosion, spreading, or signs of moisture. Because a single high-resistance pin makes the two pedal sensors disagree, this thirty-second check is the cheapest possible outcome for P2138.
- Graph sensors D and E through full pedal travel
On a scan tool, display both pedal position sensor voltages and press the pedal slowly from rest to floor. The two traces should track each other in a fixed relationship the whole way; a dropout or divergence at a specific pedal angle is the fingerprint of a worn sensor track inside the pedal.
- Flex the harness while watching the signals
Wiggle the wiring between the pedal and the firewall pass-through with live data running. A voltage that jumps when you move the harness means a chafed or broken wire — a repair, not a pedal.
- Replace the accelerator pedal assembly
If one sensor's trace glitches during the sweep, the pedal assembly is the fix — the sensors aren't serviced separately. It's typically a few nuts and one connector under the dash, one of the easier throttle-system repairs there is.
- Clear codes and verify
Clear the code, cycle the key, and confirm the car pulls cleanly through the full pedal range with no reduced-power warning. Some vehicles want a short relearn drive before throttle response feels fully normal.
DIY or shop? The pedal swap itself is genuinely easy — a home mechanic with basic tools can do it in well under an hour. What separates DIY success from parts-cannon frustration is the scan-tool graphing step, which tells you whether the pedal or the wiring is at fault before you spend money. If your scanner can't graph both pedal sensors, or the fault turns out to be in the harness, a shop's diagnostic time is money well spent on a code that can cut engine power in traffic.
Tools for the DIY steps: OBD2 scanner that graphs live data · Basic socket set and screwdrivers · Electrical contact cleaner · Multimeter · Flashlight for under-dash work
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P2138.
Frequently asked
What does 'voltage correlation' mean on P2138?
Your pedal has two sensors whose voltages must track each other in a fixed relationship as you press the pedal. P2138 means they've drifted out of that relationship — they disagree about pedal position — so the computer limits power because it can't tell which one is lying.
Is P2138 usually the pedal assembly?
It's the most common culprit — a worn spot on one sensor's track makes the signals diverge at certain pedal positions. But corroded connector pins or a damaged wire can shift one signal the same way for a fraction of the cost, so check the connector before buying a pedal.
Why does my car surge or cut power intermittently with P2138?
A worn sensor track or flaky connection often misbehaves only at certain pedal angles or temperatures. Each time the signals diverge past the limit, the computer cuts power to protect you, then may restore it when they agree again — which feels like surging or random power loss.
Can I clear P2138 and keep driving?
The code will typically return as soon as the sensors disagree again, and each event can mean sudden power loss in traffic. Because this fault directly affects throttle control, it's one to fix promptly rather than manage around.
Seeing P2138 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P2138 for my vehicleSymptoms that trigger P2138
Drivers who get this code often notice one of these — each has its own likely-causes and cost guide:
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P2138 from your phone — see our honest guide to the best OBD2 Bluetooth adapters.
Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.