Quick answer
P2138 means Accelerator/Pedal Position Sensor/Switch D/E Voltage Correlation. The controller has detected that two redundant accelerator-pedal position signals no longer agree within the relationship calibrated for that vehicle. It is a correlation fault—not proof that the pedal assembly or throttle body has failed. Save the codes and freeze frame, check the VIN for recalls or bulletins, then compare both pedal signals and test the exact reference, ground and signal circuits before replacing parts.
P2138 belongs to the electronic driver-demand system. The accelerator pedal reports what the driver is requesting; the controller decides how to produce that torque through an electronic throttle, diesel fuel and air controls, a hybrid system or an electric drive motor. The correlation principle is similar across those powertrains, but signal names, thresholds and fail-safe behavior are vehicle-specific.
What Does the P2138 Code Mean?
The generic definition is “Accelerator/Pedal Position Sensor/Switch D/E Voltage Correlation.” The controller sees both redundant inputs, but their relationship has moved outside the calibrated window.
On many vehicles, D and E correspond to the two channels inside one accelerator-pedal position (APP) assembly. GM may call the same diagnosis APP Sensor 1–2 Correlation, while other manufacturers use A/B or other labels. The letters do not prove that two separately replaceable sensors exist, and they do not identify one universal wire or connector pin.
P2138 is not simply a low-voltage, high-voltage or open-circuit code. Both channels can remain inside their individual electrical ranges and still fail the correlation test. The two traces may also use different scales, directions or even signal types; they need to maintain the OEM-defined relationship, not match each other numerically.
Do not confuse neighboring faults. P2122 concerns a low D-channel signal in the linked Ford application, while P2135 normally compares a different throttle-position A/B pair.
How the APP D/E Correlation Is Monitored
The controller continually evaluates the redundant pedal signals while the ignition is on. Depending on the vehicle, it may compare two voltages, a voltage and a frequency, percentages calculated from different transfer functions, or another OEM-defined representation. It sets P2138 when their difference or ratio remains implausible for the calibrated time and operating conditions.
One independent driver-demand channel with its own calibrated range and circuit path.
A redundant channel used to validate the first; it may not use the same raw value or slope.
Some circuits share a reference or low-reference path. One common fault can disturb both channels.
The controller may limit requested torque, acceleration, throttle opening or propulsion power when it cannot trust the pedal.
Because the monitor is designed for safety, a brief terminal dropout, water-contaminated connector or harness movement can store P2138 even when the vehicle behaves normally later. Current, pending and history status therefore matter.
Common P2138 Symptoms
- Check-engine, wrench or electronic-throttle warning: the exact indicator depends on the manufacturer.
- Reduced Engine Power or reduced propulsion message: maximum acceleration and torque may be limited.
- Delayed, inconsistent or weak accelerator response: pedal input may feel intermittent or heavily restricted.
- Cruise, traction or stability features disabled: this occurs on some applications, not every vehicle.
- An intermittent history code with normal operation: movement, moisture or terminal contact can make the disagreement temporary.
Misfires, black smoke, hard starting and rough idle are not defining P2138 symptoms. If they are present, scan for additional faults instead of forcing them into the pedal-correlation diagnosis.
Possible Causes of P2138 — Not a Parts List
Loose locks, backed-out pins, poor crimps, fretting or high terminal resistance can interrupt one channel.
Leaks at the A-pillar, windshield, cowl or sunroof drain may contaminate a body or pedal connector.
Chafing, stretching, previous repairs, pinched wiring or an intermittent open/short can upset the correlation.
One internal channel may develop dropouts or lose continuity; many vehicles service the sensor with the complete pedal.
A five-volt-reference or low-reference problem can disturb several sensors and produce companion codes.
Pedal controllers, remote-start, fleet or accessory wiring connected to an APP/reference circuit can alter the signals.
An intermediate connector or wire-pair routing problem may have a manufacturer repair procedure for the exact VIN.
PCM/ECM failure is possible but uncommon and belongs at the end of a completed power, ground, circuit and bulletin diagnosis.
Official GM documents show that P2138 has resulted from water in an instrument-panel/body connector, high-resistance terminal crimps and loss of continuity in an APP circuit. A Ford bulletin for specific Fiesta vehicles calls for a wiring modification. These examples show why replacing a pedal or throttle body from the code alone is unreliable.
How Serious Is P2138, and Can You Drive?
P2138 is a high-priority drive-by-wire fault. The controller may deliberately reduce acceleration because it cannot fully trust the driver's torque request. Reduced-power mode is a safeguard, not permission to continue normal driving.
Stop driving and arrange a tow if accelerator response is delayed, inconsistent, severely limited or accompanied by warnings that make merging, crossing traffic or maintaining speed unsafe. Move out of traffic only if the vehicle responds predictably enough to do so.
If the code is stored in history and the vehicle currently operates normally, avoid unnecessary highway or heavy-traffic driving and arrange prompt diagnosis. Fail-safe behavior differs among gasoline, diesel, hybrid and electric vehicles, so the owner's manual and OEM instructions control the decision.
How to Diagnose P2138 Step by Step
-
Make the vehicle safe
If P2138 is current and normal acceleration cannot be trusted, do not begin with a road test. Park safely, apply the parking brake and arrange towing when needed.
-
Preserve the evidence
Scan relevant modules and save current, pending, history and permanent codes plus freeze-frame data before clearing anything. Note reduced-power, reference-voltage, communication and throttle-system companion codes.
-
Check the VIN before buying parts
Use the NHTSA VIN recall lookup and current OEM service information. Certain vehicles have documented connector, crimp, continuity, water-intrusion or wiring-layout repairs.
-
Identify the exact D/E circuits
Obtain the VIN-specific wiring diagram, connector views, signal names, monitor conditions and pinpoint tests. Do not assume D and E use one universal pinout, voltage range or ratio.
-
Prioritize shared-supply faults
If a five-volt-reference or low-reference code is present, diagnose that branch first. A common supply problem can disturb both pedal channels or other sensors.
-
Inspect without erasing an intermittent fault
Before repeatedly disconnecting parts, inspect the pedal connector, intermediate body connectors and harness for water, corrosion, terminal push-out, loose locks, chafing, taut wires and aftermarket splices. Repair the source of any leak.
-
Graph both APP signals together
With the vehicle secured, transmission in Park or Neutral and ignition on, slowly press and release the pedal while graphing both OEM APP PIDs. Each trace should be smooth and repeatable and maintain the vehicle-specific relationship. Watch for dropouts while gently moving suspect harness sections.
-
Test reference, return and signals
Backprobe only with the correct connector view and high-impedance equipment. Follow OEM thresholds for reference supply, low-reference voltage drop and each signal. Never apply battery voltage or join the two signal wires.
-
Isolate the pedal, harness and controller
Use the OEM pinpoint test to determine where the mismatch begins. Do not condemn the throttle body or PCM from P2138 alone, and do not rely on a static resistance test for an intermittent Hall-effect circuit.
-
Repair and verify the monitor
Complete any required setup, repeat the full pedal sweep, rescan for current and pending codes and confirm normal torque response. Road-test only after static checks show stable correlated signals.
Avoid shortcuts: do not publish or use a universal 0.5–4.5 V rule, a fixed D/E ratio, a jumper or resistor intended to fool the monitor. Some manufacturers use different signal types and scaling.
How to Fix P2138
- Repair a connector or terminal: correct terminal tension, crimp, pin retention or corrosion using the OEM-approved method.
- Correct water intrusion: repair the leak source, then repair or replace damaged terminals and harness sections.
- Repair the harness: restore an open, short, chafed section, strained wire pair or application-specific routing issue.
- Remove or rewire interfering accessories: follow the manufacturer procedure when aftermarket equipment shares APP, reference or low-reference circuits.
- Replace the pedal/APP assembly: only after the pinpoint test proves an internal signal fault. Many APP sensors are not serviced separately.
- Replace a throttle body or separate TPS: only when the vehicle's code description and test results identify that assembly; P2138 alone is insufficient.
- Update or replace the controller: only when an applicable bulletin directs calibration or all circuit, pedal, power and ground tests prove a controller fault.
After any repair, perform only the setup, relearn or programming specified for that vehicle. Clearing the light without repeating the correlation monitor is not repair confirmation.
Using iCarsoft CR MAX for P2138
On supported vehicles, CR MAX can scan all available modules, record codes and freeze frame, display and graph supported APP and throttle PIDs, and run applicable electronic-throttle active tests or service functions. Comparing both pedal traces on one screen can expose an intermittent dropout or loss of correlation.
CR MAX uses a direct 16-pin cable for the vehicle connection; Wi-Fi is used for scanner software updates. It does not replace the VIN-specific wiring diagram, a high-impedance meter or scope, terminal test tools, nor the OEM safety procedure. Live-data names, active tests and relearn functions vary by year, engine and ECU.
Recommended diagnostic platform for P2138
iCarsoft CR MAX Car Diagnostic Tool
Save scan evidence, graph supported pedal and throttle data, and run available electronic-throttle tests while verifying the physical circuit with the required tools.
Check current price & availability · lifetime free scanner software updates
View iCarsoft CR MAXCheck CR MAX compatibility by VINCoverage matters: send iCarsoft the VIN and the exact APP live-data, throttle test or relearn function you need before purchase. See the vehicle and function coverage and keep the tool current through the CR MAX Wi-Fi update guide.
How Much Does It Cost to Fix P2138?
P2138 does not identify one failed part, so an honest estimate begins with circuit diagnosis. The following are broad 2026 US planning ranges for parts and labor, not a quote. Do not add the rows together; diagnosis should identify one confirmed path. Always check the VIN for recalls, extended coverage or service campaigns before authorizing paid work.
| Confirmed path | Typical US estimate |
|---|---|
| Professional drive-by-wire electrical diagnosis | $120–$250 |
| Connector, terminal or localized harness repair | $120–$600 |
| Accelerator-pedal / APP assembly replacement | $180–$650 |
| Separately serviceable throttle-position sensor, where fitted and proven | $180–$300 |
| Electronic throttle-body assembly, where proven | $400–$1,100 |
| PCM/ECM replacement and programming, rare and only after proof | $700–$1,800 |
Water-leak correction, difficult connector access, regional labor rates and programming can change the total. Some affected vehicles have had recall or special-coverage repairs, so a VIN check can matter more than a generic price estimate.
Repair Confirmation and Prevention
P2138 is not prevented by a universal throttle-body cleaning interval. More useful prevention is keeping the pedal area and body connectors dry, correcting windshield/cowl/sunroof leaks, securing the harness away from rub points and avoiding aftermarket splices into APP, five-volt-reference or low-reference circuits.
After repair, graph both pedal signals through several slow sweeps, gently move the repaired harness, verify normal driver-demand response, rescan all relevant modules and check for returning current or pending codes. Complete the OEM monitor or road test only after static testing shows reliable correlation. A permanent DTC may remain until the monitor passes.
Related Throttle and Pedal Codes
Other possible companions include P2121, P2123, P2126, P2127, P2128, P2106 and P2110. Their availability and exact wording vary by vehicle, so read every code in its OEM context.
P2138 Frequently Asked Questions
What does code P2138 mean?
P2138 means Accelerator/Pedal Position Sensor/Switch D/E Voltage Correlation. The two redundant driver-demand signals no longer maintain the relationship calibrated for that vehicle. It is not proof that a specific part has failed.
Does P2138 point to the accelerator pedal or the throttle body?
On many vehicles P2138 compares two channels in the accelerator-pedal assembly, but generic D/E labels are not a universal component map. Confirm the code description, wiring diagram and PID names for the exact VIN before deciding which assembly to test.
Can I drive with P2138?
Do not rely on the vehicle when accelerator response is delayed, inconsistent or severely limited, or when reduced-power behavior makes traffic maneuvers unsafe. Move out of danger if the response is predictable enough, then arrange a tow. Even an intermittent history code deserves prompt diagnosis.
Can wiring or connector corrosion cause intermittent P2138?
Yes. Official manufacturer documents identify poor terminal crimps, water intrusion, corroded intermediate connectors, loss of APP-circuit continuity and application-specific wiring layout as real P2138 causes.
Should the D and E voltages be identical?
No. The two channels may use different voltage scales, directions, ratios or signal types. Compare them with the OEM scan-data description and thresholds; smooth but unequal traces can be normal.
Will cleaning the throttle body fix P2138?
Not usually. P2138 is a correlation fault between redundant position signals. Cleaning may be relevant to a separate throttle-plate performance problem, but it does not repair a damaged pedal circuit, terminal, reference supply or sensor channel.
How much does it cost to fix P2138?
Broad US planning ranges are about $120–$250 for diagnosis and roughly $120–$1,800 for the confirmed repair path. A connector repair, pedal assembly, throttle body and controller are alternatives, not parts to replace together. Check the VIN for recall or special-coverage eligibility first.
Can iCarsoft CR MAX help diagnose P2138?
On supported vehicles, CR MAX can scan relevant modules, save codes and freeze frame, and graph available APP and throttle PIDs. Supported active tests and relearns vary by vehicle, so confirm the exact function by VIN. Physical circuit testing and OEM information are still required.
Technical and cost references
- SAE J2012DA diagnostic-code definitions and Ford 2024–2025 gasoline OBD operation summary – standardized naming and an OEM APP signal-correlation example.
- GM official examples: water intrusion and APP connector diagnosis, 2014 Cadillac ATS terminal-crimp recall and Malibu/LaCrosse/Regal special coverage.
- Ford TSB 13-3-19 – application-specific APP connector and wiring repair; Volvo recall R10170 – pedal-circuit water intrusion in an electric vehicle.
- Official iCarsoft CR MAX product page – verified full-system scan, live-data, active-test, service-function and lifetime-update information; coverage varies by VIN.
- Current US cost anchors: throttle-position sensor, throttle body and PCM replacement. Connector, pedal and local labor estimates vary by VIN and region.
Editorial note: This article provides general educational guidance, not a substitute for the service information, safety instructions and specifications for a specific VIN. Never bypass redundant pedal circuits or apply battery voltage to a signal wire. Prices are US planning ranges and can change. Confirm recalls, product coverage, repair procedures and local pricing before work begins.
