TechTips #1 – Electronic Throttle Body Troubleshooting

[Music] your customer arrives with a poor or rough idle concern and the check engine light may not be illuminated could this still be a problem with the electronic throttle body and while there are other potential causes for this customer's concern today i'd like to focus on the electronic throttle body it's testing and if necessary it's replacement and as any good diagnostician knows before we begin testing we need to understand how it works the electronic throttle body works hand in hand with the accelerator pedal position sensors as the driver operates the pedal whether he's accelerating or decelerating or maintaining a steady speed these sensors submit a signal to the ecm to let the ecm know what he wants based on these inputs and other information the ecm can send out a signal of its own to the electronic throttle body specifically it's going to operate a small dc motor that's contained in the assembly i also want you to notice the reduction gear set contained in the assembly connecting the motor to the throttle plate this gives the ecm some very precise control of the throttle plate opening allowing it to change the throttle plate angle as little as one half of a degree at a time now for everything that the ecm does it requires feedback so that it can know that what it commanded actually happened in the case of the electronic throttle body this feedback is provided by a pair of redundant throttle position sensors also contained in the assembly another job that the ecm has is to keep an eye on the various inputs and outputs to make sure that they're working as they should if it detects a problem it may set a diagnostic trouble code or dtc and may even turn on the check engine light to alert the driver in some cases it will put the vehicle into limp in mode which means that the vehicle can still be started but its operating speed is limited the first thing to do if you suspect a problem with the electronic throttle body is to connect your scan tool and check the engine control module for any stored diagnostic trouble codes or dtcs keep in mind that codes can be pending which means they won't turn on the check engine light so it's always a good idea to check for yourself and if you do find any code stored use the diagnostic flow chart to help you identify the cause if no codes are found proceed with your visual inspection remove the intake air duct to access the throttle body [Music] [Music] visually inspect the bore of the throttle body and the throttle plate it's not unusual to see deposits building in the throttle body near the throttle plate as these deposits build it can reduce airflow past the throttle plate and into the engine the ecm can only correct for these buildups but so much so it's not a bad idea to recommend to your customer that the throttle body be cleaned periodically about every fifty thousand miles or so or as outlined in the oe maintenance schedule also remember that when cleaning the throttle body the ecm has relearned a new initial position for the throttle plate when you remove the deposits it's going to allow more air flow into the engine and could impact idle speed in which case you'll need to perform an idle relearn as outlined in the service information now on to inspecting the electrical side of the throttle body a voltmeter or an ohmmeter can be used to perform many of these circuit tests but i prefer to use a scope in order to catch any dropouts in the signals that the other tools may not catch let's begin by checking the ecm's ability to operate the throttle body motor using my scope i'm going to connect one channel to the motor positive input and one to the motor negative input right at the connector located at the throttle body the ecm controls the throttle plate by sending a pulse width modulated signal to the motor do not try to move the throttle plate by hand while the key is on damage to the throttle body and even to your fingers could occur listen closely to the motor as the pedal is moved for any abnormal noise noisy motors are a sign of bad motors now if you do note any issues in the throttle body motors operation or the ecm signals to it go back and make sure that the accelerator pedal position sensor signals are nice and smooth going to the ecm the ecm can only act based on the information it's given so if there are any glitches in these signals it could impact the motor's operation with the motor operation inspected we can move on to the sensors that provide the feedback to the ecm that is the sensors that lit the ecm know the throttle plate is moving the way it wants it to these are the throttle position sensors and can be tested by watching the signal return to the ecm as the throttle plate is moved the voltage should increase and decrease smoothly any dropouts in the signal indicate a failing sensor requiring replacement of the assembly if you've proven that the throttle body is defective it's time to consider a replacement now you can go direct oe or you can choose a part from the aftermarket just be careful not all aftermarket parts are the same be sure to choose a part that provides the same oe form fit and function so that you can guarantee a quality dependable repair anything less could result in poor performance even a customer come back that's why i'm choosing a door last throttle body for this project duralast is a dependable oe quality brand that is precisely calibrated to meet or exceed oe specifications giving you a true oe form fit and function and if there is a known defect in the original design duralast re-engineers the product to address those concerns to change out the throttle body follow the oem procedures for removal some like this corolla have cooling passages incorporated in the housing so we'll clamp off those lines before we disconnect them [Music] [Music] [Music] [Music] [Music] [Music] remove the old gasket and clean the gasket surface most designs use a plastic manifold and a rubber gasket like this one but it's still important to remove any fluids from the gasket's groove to ensure that the gasket doesn't try to shift or roll when it's compressed install the gasket and then carefully place the throttle body in position [Music] [Music] start the mounting bolts to hold it in place and tighten just enough to lightly seat the throttle [Music] body [Music] [Music] use a torque wrench to complete the tightening sequence following the order and torque specifications set forth by the manufacturer reinstall any coolant or vacuum lines then the wiring connector and finally reinstall the air intake assembly [Music] but we're not quite done yet many vehicles require that the idle speed be relearned anytime that the throttle body is replaced sometimes even after cleaning you're only going to know for sure if you check the vehicle service information and see if that process is listed as the step you have to take before completing this repair the first step in relearning the idle on this toyota is to start the engine and allow it to come up to normal operating temperature and that makes sense doesn't it cold idle speeds tend to be a little higher than warm idle speeds so if we try to perform the relearn while the vehicle is still cold it could affect what the final outcome will be next turn the engine off and make sure that all the accessories are off the ac radio anything that is placing an above normal electrical load on the system and that too makes sense the higher the electrical loads we place on the alternator the more work it has to do and the ecm is going to adjust idle speed to compensate now we need to tell the ecm to go into self-learn mode turn the ignition key to the on position and then bring it all the way off repeat the cycle one more time and then start the engine now with your foot on the brake fully engage the parking brake and put the vehicle into drive the ecm will relearn the correct idle speed but be patient it might take a few minutes and after your relearn has been successfully performed and prior to returning it to the customer make sure that you take it for a test drive and verify your repair to avoid a potential comeback one more way you can make sure your customer stays happy use a part that's going to provide them with oe form fit and function with door last you get oem performance or better at an after market price to learn more about the entire line of door last parts visit www.doorlastparts.com thanks for watching [Music] you

Channel: Motor Age

Views: 664,132

Keywords: motor age, the trainer, automotive repair, car repair, auto how to, how to fix my car, auto tech, auto technician, auto service professional, duralast, autozone, throttle body, fuel injection

Id: 61lLTJJMAB0

Length: 13min 53sec (833 seconds)

Published: Mon Nov 16 2020