The Throttle Position Sensor (TPS) is a critical component in your Honda’s engine management system. Located on the throttle body, the TPS monitors the position of the throttle plate and relays this information to the Engine Control Unit (ECU). This sensor input is crucial for the ECU to accurately determine engine load and driver demand, working in conjunction with other sensors like the Mass Airflow Sensor (MAF), Manifold Absolute Pressure (MAP) sensor, and oxygen sensors. By understanding the throttle position, the ECU can precisely control fuel delivery, ignition timing, and idle speed, ensuring optimal engine performance and efficiency. Think of the TPS as the ECU’s direct line to your right foot, translating your accelerator pedal input into actionable data for the engine.
Electrically, Honda TPS sensors operate as variable resistors, also known as potentiometers. At rest, with the throttle closed, the sensor exhibits a high resistance. As you depress the accelerator pedal and open the throttle, this resistance decreases, allowing more voltage to flow to the ECU. This change in voltage is interpreted by the ECU as a change in throttle position. A healthy TPS will exhibit a smooth and linear voltage increase as the throttle opens, typically ranging from approximately 0.5 volts DC at closed throttle to around 4.5 volts DC at wide-open throttle.
Accurate voltage readings are essential for proper TPS function. This diagram illustrates the expected voltage range from closed to wide open throttle.
Symptoms of a Failing TPS
When a TPS begins to malfunction, it can send inaccurate or erratic signals to the ECU, disrupting the engine’s ability to operate efficiently. One of the most common indicators of a TPS problem is the illumination of the “Check Engine” light, which may be accompanied by diagnostic trouble code (DTC) #7 specifically pointing to the TPS circuit.
Beyond the check engine light, several driveability issues can signal a failing TPS:
- Hesitation, Stumbling, or Misfiring: Particularly at low RPMs, a faulty TPS can cause the engine to hesitate or stumble upon acceleration. This occurs because the ECU is receiving incorrect throttle position data and miscalculating fuel and ignition requirements.
- Poor Fuel Economy: Inaccurate throttle position readings can lead to the ECU injecting too much or too little fuel, resulting in decreased fuel efficiency.
- Inconsistent Idle: The engine may idle erratically, too high, or too low, as the ECU struggles to maintain a stable idle speed without accurate TPS data.
- Dead Spots or Intermittent Issues: Sometimes, a TPS may only malfunction at specific throttle positions. You might experience stumbling or hesitation only when the throttle is at, for example, 25% open, while the rest of the throttle range feels normal. This indicates a “dead spot” or inconsistency within the sensor’s resistive track.
Testing Your Honda TPS
Diagnosing a TPS issue is typically straightforward and can be done with a basic multimeter. The Honda TPS utilizes a three-wire system, each wire serving a distinct purpose:
- GREEN Wire: DC Negative Ground – This wire provides the ground connection for the sensor.
- RED Wire: DC Signal Output to ECU – This is the critical signal wire that transmits the throttle position voltage reading back to the ECU. This is the wire you will measure for calibration and testing.
- YELLOW Wire: 5V DC Positive Reference Voltage – This wire supplies a constant 5-volt reference voltage to the TPS from the ECU, ensuring consistent sensor operation. You should always read 5V on this wire when the ignition is in the “ON” or “ACC” position.
Understanding the wiring of your Honda TPS is crucial for accurate testing and diagnosis. This diagram shows the standard wire colors and their functions.
Before you begin testing, ensure your key is in the ignition and turned to the “ACC” (Accessory) position to power the sensor.
Ground Wire Test (Green Wire):
- Set your multimeter to the continuity setting (often symbolized by a –>I– symbol or a sound wave icon (((( which beeps when continuity exists).
- Connect the negative (black) lead of your multimeter to a known good ground, such as the negative battery terminal.
- Connect the positive (red) lead of your multimeter to the GREEN wire of the TPS connector.
- Your multimeter should indicate continuity (beep or show a near-zero resistance reading), confirming a good ground connection.
5V Reference Voltage Test (Yellow Wire):
- Set your multimeter to DC Voltage mode.
- Connect the negative (black) lead to a known good ground.
- Connect the positive (red) lead to the YELLOW wire of the TPS connector.
- You should read approximately 5V DC. A reading significantly lower or higher indicates a problem with the reference voltage supply from the ECU or a wiring issue.
TPS Signal Output Test (Red Wire) and “Dead Spot” Check:
- Set your multimeter to DC Voltage mode.
- Connect the negative (black) lead to a known good ground.
- Connect the positive (red) lead to the RED wire of the TPS connector.
- With the throttle fully closed, you should read approximately 0.5V DC.
- Slowly and smoothly open the throttle to wide-open throttle. As you open the throttle, observe the voltage reading on your multimeter. It should increase smoothly and steadily, without any sudden jumps, drops, or gaps. At wide-open throttle, you should reach approximately 4.5V DC.
- Pay close attention to the voltage reading throughout the throttle range. Any erratic voltage fluctuations, sudden drops to zero, or “dead spots” where the voltage doesn’t change as you move the throttle indicate a faulty TPS sensor.
Wiring Reversal and Common Mistakes:
- Reversed Voltage Readings: If you find your voltage readings are reversed (approximately 4.5V at closed throttle and 0.5V at wide-open throttle), it is highly likely that the GREEN and YELLOW wires are reversed in the TPS connector. Double-check your wiring and correct any misconnections.
- TPS and MAP Sensor Plug Swap: Another common mistake, particularly when working in the engine bay, is accidentally swapping the TPS connector with the Manifold Absolute Pressure (MAP) sensor connector. Ensure that each sensor has its correct corresponding plug connected.
ECU Reset After TPS Work:
In some cases, especially if you disconnected the TPS while the ignition was on during testing, you may need to reset the ECU to clear any stored diagnostic trouble codes (like code 7) and ensure the engine computer properly recognizes the new or adjusted TPS. A simple ECU reset procedure for many Honda models involves:
- Disconnecting the negative battery cable.
- Locating the “Hazard” fuse (typically 10A) in the under-hood fuse box and removing it.
- Waiting for approximately 20 seconds.
- Reinstalling the “Hazard” fuse and reconnecting the negative battery cable.
While resetting the ECU via fuse removal is a common practice, some newer vehicles may benefit from or require diagnostic tools for more comprehensive resets, particularly when dealing with systems like TPMS (Tire Pressure Monitoring System) or other advanced features. For basic sensor replacements like the TPS, the fuse method is often sufficient. However, if you are working on a 1998 Honda Accord and encountering TPMS issues, note that OBD2 tools are generally not used for resetting TPMS on vehicles of that era, as TPMS systems were less common and less sophisticated then.
TPS Removal and Installation
TPS Removal:
- Throttle Body Removal (Optional but Recommended): While it’s possible to remove the TPS with the throttle body still on the intake manifold, removing the throttle body provides significantly easier access and workspace. To remove the throttle body:
- Disconnect the intake air ducting from the throttle body.
- Disconnect the throttle cable and cruise control cable (if equipped).
- Disconnect the TPS wiring plug and any other vacuum lines connected to the throttle body.
- Remove the two 12mm bolts and two 12mm nuts that secure the throttle body to the intake manifold.
- Be prepared to replace the throttle body gasket upon reinstallation.
- TPS Fastener Removal: The TPS is typically secured to the throttle body with two screws. Depending on the year and model of your Honda, these screws may be:
- Torx Screws: Later models often use Torx head screws.
- Machine Screws with No Head: Older models may use machine screws with smooth, rivet-like heads. For these, you will need to carefully create a slot in the screw head using a Dremel tool with a cutoff wheel or a hacksaw blade. Then, use a flathead screwdriver to unscrew them.
The TPS is typically held in place by two screws. Note the screw type on your sensor, as older models may require slotting for removal.
TPS Installation and Calibration:
- Install the New TPS: Align the tab on the new TPS sensor with the corresponding slot on the throttle body shaft. Rotate the TPS counter-clockwise until the bolt holes line up.
- Finger-Tighten Screws: Install the TPS mounting screws and tighten them finger-tight, just enough to hold the sensor in place but loose enough to allow for slight swivel adjustment.
- Reinstall Throttle Body (If Removed): If you removed the throttle body, reinstall it onto the intake manifold using a new throttle body gasket. Reconnect all vacuum lines, coolant lines (if applicable), throttle cable, and cruise control cable.
- Connect TPS Wiring Plug: Connect the wiring plug to the newly installed TPS sensor.
- Voltage Calibration:
- Connect the negative lead of your multimeter to a good ground.
- Connect the positive lead to the RED signal wire of the TPS connector.
- Turn the ignition to the “ACC” position.
- Gently swivel the TPS sensor on the throttle body until you achieve a voltage reading of 0.5V DC on your multimeter.
- Once you have achieved 0.5V, carefully tighten the TPS mounting screws to secure the sensor in its calibrated position.
- Voltage Verification: After tightening the screws, re-verify the voltage readings at both closed throttle (should be approximately 0.5V) and wide-open throttle (should be approximately 4.5V) to ensure proper calibration and sensor function.
DPFI (Dual Point Fuel Injection) TPS Considerations
It’s important to note that Honda’s DPFI (Dual Point Fuel Injection) systems, found on some earlier models, utilize a different type of TPS sensor compared to the MPFI (Multi-Point Fuel Injection) systems common on later models. The DPFI TPS sensor rotates in the opposite direction of MPFI sensors. Because of this reversed rotation, the wiring is also reversed to compensate.
DPFI TPS sensors have reversed wiring compared to MPFI sensors due to their opposite rotation. Be aware of this difference when replacing a DPFI TPS.
If you are converting from a DPFI system to an MPFI setup or performing an engine swap to a B-series engine (which are typically MPFI), you MUST reverse the GREEN and YELLOW wires at the TPS connector to ensure proper TPS operation with the MPFI system.
When sourcing a replacement TPS sensor for a DPFI system, be sure to specifically order a TPS designed for DPFI applications. MPFI TPS sensors will not work directly with DPFI systems due to the reversed rotation and wiring. While some enthusiasts have explored disassembling and attempting repairs on DPFI TPS sensors, these repairs are often not reliable or long-lasting. Purchasing a new, correct DPFI replacement sensor is generally the best solution. Manufacturers like Omni Power offer aftermarket TPS sensors designed for Honda DPFI systems.
By understanding the function, diagnosis, and replacement of your Honda’s Throttle Position Sensor, you can effectively troubleshoot engine performance issues and ensure your vehicle runs smoothly and efficiently.
