P2138 – Meaning, Causes, Symptoms, & Fixes
Code P2138 Definition
The voltage readings going to the Engine Control Module (ECM) from the throttle body position sensor and accelerator pedal position sensor do not match each other.
What Does P2138 Mean?
On older vehicles, the throttle body was connected to the accelerator pedal via a throttle cable which was a mechanical link between the two. When you pushed the accelerator pedal the throttle body opened, simple as that. As vehicles became more powerful, emissions controls became stricter and better fuel mileage was a requirement, there needed to be a way for the Engine Control Module (ECM) to control the throttle more precisely. Thus, the drive by wire system was introduced. In this system, the accelerator has a sensor on it that detects how hard you are pressing on the accelerator pedal, and based on the information the ECM receives it commands the throttle body to open based on your accelerator input. This system can also be used for traction control; if the ECM sees that the wheels are slipping, it can limit throttle opening in order to gain control of the vehicle. When code P2138 is set, the ECM has found that the throttle position sensor and accelerator pedal position sensor aren’t producing the expected signals that they should be. When the ECM detects this, it may put the vehicle in a fail-safe condition that limits throttle opening to 5-15%. It may require the vehicle to be towed to a repair facility.
What Are The Symptoms Of Code P2138?*
- Check Engine Light
- Very little acceleration
- Vehicle may not start
- Vehicle may stall
*No noticeable adverse conditions in some cases
What Is The Cause Of Code P2138?
- Throttle position sensor
- Throttle body actuator
- Accelerator pedal position sensor
- Damaged wiring
- Poor electrical connections
How Serious Is Code P2138? – Severe
This trouble code can cause the vehicle to lose throttle response. If this happens at the wrong time, it could result in a wreck. Immediate repair is the only recommendation.
Code P2138 Common Diagnosis Mistakes
Replacing the throttle body without checking for poor wiring or loose connections.
Tools Needed to Diagnose:
- Basic Hand Tools
- Vehicle Specific Service Manual
How To Diagnose And Repair Code P2138?
Difficulty of Diagnosis and Repair (4 out of 5)
- Check to see if there are any other codes along with P2138 and clear your Check Engine Light with FIXD.
- Check the freeze frame data in order to pinpoint the issue.
- Check for Technical Service Bulletins (TSBs) If your manufacturer has had issues with this code, there may be a bulletin that will tell you what to replace.
- Check the wiring to the throttle body for chafing, disconnection, or pins that have backed out of the connector for the throttle body or throttle body position sensor. Tech Tip: Do Not unplug the throttle body. Doing so may make it where the vehicle will have to have a throttle body relearn performed. Sometimes you can do this without a scan tool, but many manufacturers require a diagnostic scan tool to perform a throttle body initialization.
- Check the wiring to the accelerator pedal position sensor for chafing, disconnection, or pins that have backed out of the connector. Tech Tip: Do Not unplug the accelerator pedal position sensor. Doing so may make it where the vehicle will have to have an accelerator pedal relearn performed. Sometimes you can do this without a scan tool but many manufacturers require a diagnostic scan tool to perform an accelerator pedal position sensor initialization.
- If all these check out good, consult your vehicle-specific service manual and perform a component inspection of the throttle body position sensor and accelerator pedal position sensor. This will usually have you check the signal voltage of the sensors. For the throttle position sensor, it should start at approximately .5V and go up to 5V or vice versa based on which sensor your testing. The accelerator pedal position sensor will start with a low voltage and increase the voltage as the pedal is depressed.
Estimated Cost of Repair
For error code P2138, one or more of the below repairs may be needed to solve the underlying issue. For each possible repair, the estimated cost of repair includes the cost of the relevant parts and the cost of labor required to make the repair.
- Throttle body actuator $570-$700
- Throttle position sensor $170-$230
- Accelerator pedal position sensor $130-$200
- Wiring repair/replacement $100-$1000