How To Diagnose A Faulty ECU With No Communication

hi guys tim here from ecu testing in this video i'm going to show you how to diagnose a faulty engine ecu when you have no communications with the control unit we will cover what inputs and outputs are required and how to confirm the root cause of the failure let's get started so what do you need first well that's an obvious one you need the engine ecu to be correctly connected to the vehicle if it's previously been removed make sure all connectors are secured and all pins are straight and intact the battery needs to be in good working order with a voltage of around 12.6 volts that's a static voltage with the engine off so the first thing to look at is the ground contacts the battery is connected to the engine ecu through the vehicle's wiring loop the negative side is also connected to the vehicle's chassis and body at various ground points these ground wires in the loom tend to be thicker and there may be multiple ground wires connected this is so they can handle a higher electrical current flowing through the engine ecu also needs a permanent positive battery connection this connection is usually fused so we'll normally go through a fuse box or body control module before it gets to the engine ecu this voltage can be tested directly at the engine ecu again using a multimeter refer to the vehicle manufacturer's technical information for connector and pin designations usually found on the wiring diagram as these are different on most makes and models of vehicle this voltage should match the battery voltage previously tested if no voltage is present check the relevant fuses and continuity test the wiring a good wire should have a resistance as close as possible to zero ohms if the wire is reading open circuit or has a very high resistance this is an indication you have a wiring fault however this is not always the best way to test for wiring issues a better way of testing for wiring issues is to carry out a voltage drop test for example the battery voltage is 12.6 volts but the voltage at the ecu pin has been measured to be 11.3 volts this would indicate a potential fault with the wiring this should then be further investigated and also check the grounding points on the vehicle [Music] at this point the ecu is still in standby mode and not fully powered up the next stage in its power up sequence is when the ignition switch is turned to the on position this action provides another fused positive feed matching the battery voltage to the ecu this is sometimes through a separate ignition relay but the theory is the same once again this voltage can be measured directly at the ecu and should only be present with the ignition key in the on position the voltage reading should be the same as your battery voltage if the voltage isn't present or isn't the same voltage as the battery check the fuse first and then the relevant wiring for issues once the engine ecu has its required inputs grounds permanent battery feed and its switched ignition voltage in most instances the ecu will then supply a switched ground output to the coil side of the main relay at contact 85 this relay can also be called the engine control relay or dme relay dependent on the make and model of the vehicle measure this switched ground with your multimeter with the ignition off the relay coil contact 85 should read the same as the battery voltage assuming that the relay contact 86 has this voltage present when the ignition is switched on the ecu should pull this voltage to ground zero volts as this is an output signal from the ecu if this switched ground voltage is missing and all previous checks are okay this may indicate a fault with the engine ecu assuming that there is a good battery voltage supply at relay coil contact 86 and the common contact 30. this switched ground zero volt output from the ecu to coil contact 85 on the relay will cause the common contact 30 to short the normally open relay contact 87 it is then supplied back to the ecu through a fuse sometimes on thicker or multiple wires for a higher current handling capacity this voltage is also used to supply power to various engine related sensors and actuators using the multimeter check all points where the main relay supplies the positive battery voltage tip if this voltage doesn't exist then check the main relay itself the fuses and the relevant wiring if a lower voltage is present in the battery supply this may indicate a wiring fault or a faulty sensor or actuator this is pulling the voltage down [Music] at this point the engine ecu is powered up it should therefore be outputting a controller area network can bus this is what the ecu uses to communicate with other control modules on the vehicle and also with diagnostic equipment other communication protocols such as flexray kwp2000 linbus and most can also be used check the vehicle manufacturer's information to confirm this the can bus consists of two whites kanhai and can love and these are twisted together in the wiring loom so usually quite easy to identify a quick test can be carried out on the canvas using a two channel oscilloscope connect the two oscilloscope leads to the scope connect the grounds together and connect them to a good ground point on the car probe the two cam lines at the same time and observe the signal on the display the two signals should be a mirror image of each other with one side pulled high and the other pulled block if no signal is present then this would suggest a fault with a control module on the communication bus either with the engine ecu or another control module this can be proven by systematically disconnecting various control modules and monitoring if the can bus signal returns so to summarise if you're experiencing symptoms of no communication with your engine ecu ensure that the ecu has all the relevant inputs outlined in this video if any are missing then rectify these issues and recheck if all inputs are present and the ecu isn't outputting a switched ground for the main relay or the can bus signal is missing then this could be due to a fault with the engine ecu itself if you've got any questions drop them in the comments below and we'll get back to you as soon as we can remember if you're experiencing issues with your ecu we're here to help if you'd like to send your unit in to us please visit our website for more details thanks for watching we'll see you in the next video you

Channel: ECU TESTING

Views: 435,198

Keywords: car not starting, ecu fault, ecu fault symptoms, diagnose ecu, how to diagnose ecu problems

Id: Y3aoD5BMxQw

Length: 6min 49sec (409 seconds)

Published: Wed Aug 18 2021