Honda Civic throttle sensor problems can arise from a number of issues. Whether you are completing a Honda engine swap, or you have a Civic P2122 trouble code, this OBDII guide can help. Today I’ll be showing you how to troubleshoot, test and replace your Honda Civic TPS sensor in a 1997 Honda Civic EX with a D16Y8 motor.
This SOHC engine is very common, and testing the Civic throttle position sensor is simple. Using this guide, you can clear your Civic P2122 check engine light. So if you have a Honda Civic check engine light, grab an OBDII scan tool and check your code.
Honda Civic P2122 – Test your TPS
The P0122 Honda OBDII Diagnostic Trouble Code occurs when your Honda Civic D16 ECU receives a throttle position signal that’s lower than what it expects. The throttle position sensor (TPS) is a huge part of how the Powertrain Control Module and how it controls fuel and spark in relation to closed loop operation, this trouble code can put your car into limp mode.
The P2122 code means that the vehicle’s on-board computer has detected low voltage in the throttle position sensor (TPS), which is usually below 0.17 volts.
The P0122 check engine code can cause serious engine operation issues and hinder your gas mileage and efficiency. Because your ECU does not know exactly what the throttle blade is doing or how much throttle is being fed, it won’t know how to run your car.
How do I test my Honda Civic throttle position sensor? This guide will show you how to test the sensor for power and ground, and test the range of the voltage output from the TPS signal wire.
What is the Throttle Position Sensor?
The TPS sensor is basically a three wire potentiometer that measures the amount the throttle body is being opened. This signal is converted to a signal that your Honda D16Y8 P2P ECU can recognize and use to operate closed loop mode.
Using the throttle position sensor signal as well as other important engine references, the P2P ECU in your Honda Civic “aims” for a exhaust air/fuel ratio of 14.7:1. That’s roughly 14 parts fuel for one part air that is considered automotive “stoich”, which is what closed loop operation or closed loop mode is for.
Without this important reference of throttle blade position, the job of running your engine efficiently becomes almost impossible. And when the voltage from this sensor falls below what you ECU expects, you will get a Civic P2122 code.
What causes the Civic P2122 DTC Code?
Your P2P or similarly chipped VTEC ECU has received a reference signal from your TPS that’s much lower than what it expected. Either your throttle position sensor has gone bad or there’s problems with the power and ground to the sensor.
There could also be a short or a break in the wire between your ECU and the TPS itself that causes your P0122 Honda code.
How To Test your Civic Throttle Position Sensor
I will be breaking out the procedure on how to test your Honda Civic Throttle Position Sensor into four different steps, starting below. As usual, any modifications or testing you perform on your own car are not my responsibility. If you don’t feel like this is a job you can perform, take your car to an experienced auto shop.
Unclip the top half of the factory Honda airbox by undoing the metal band clips that hold the upper cover to the lower assembly. Need my in-depth guide to testing a Civic TPS? Check it out here!
Now you will need to disconnect the Air Intake Temperature sensor that’s mounted in your factory airbox.
Now pull up on the upper cover to remove and expose the air filter underneath the top of the airbox. Remove your factory filter to reveal the throttle body and complete lower airbox assembly.
There’s going to be one 8mm bolt that holds the left side ( passenger side ) of the lower assembly in place, remove this bolt now.
Disconnect the vacuum hoses that are connected to the front of the airbox, and now you are ready to pull up and away on the lower assembly.
Here’s a look at the intake manifold and throttle body opening, you are now ready to move onto the first part of the testing procedure. You might also want to replace or test your Civic IAT while you are at it.
Checking for TPS Power
Take some time to familiarize yourself with the throttle position sensor and the three pin weatherproof connector and wires. Put the key to the “ON” position but do not turn the engine on, your sensor should now be powered.
Take your voltmeter and put the black lead to the battery ground, now put the red lead to the third pin or PIN 3. This yellow wire with red stripe should be sending you 5 volts of switched power and is needed for your Honda D16 TPS to work properly.
Now switch the red lead to the battery terminal and put the black lead to first pin or PIN 1. This green wire with black stripe should have a ground present, which will allow your TPS to receive power.
Checking for TPS Signal
It’s the moment of truth, the moment where you find what the source of your Civic P2122 trouble code is. Take your voltmeter and secure the black lead to the negative terminal on your battery. Now with one hand backprobe the middle red wire with black stripe for the signal from your throttle position sensor.
You should see a voltage values here, which means you are ready to test the operation of your throttle position sensor. Using your other hand, deflect or push down on the throttle body blade to manually open your throttle body from the engine bay.
This testing method is the best and easiest way to determine what next steps need to be taken to resolve your Civic P2122 DTC trouble code. Using your hands to manually open your throttle blade, the voltage reading on your multimeter should range from less than one volt all the way to 3.6 to 4.8 volts DC. Make sure you have between the 3.6-4.8 voltage range at Wide Open Throttle (WOT) and less than one volt with the throttle blade closed.
Now slowly open and close the throttle, going slowly so that you can see the voltage rise and fall in accordance of the throttle blade opening and closing. There should not be any jumps or spikes in the voltage and it should seem like a smooth transition from closed to WOT.
Replace your throttle position sensor or the throttle body completely to resolve your P0122 OBDII DTC trouble code!
Have any questions? Let me know below!
Thanks for reading!
