AUTOINFORM ONLINE MAGAZINE: HOW TO DO PCM TESTING ON VEHICLES

AUTOINFORM ONLINE MAGAZINE: HOW TO DO PCM TESTING ON VEHICLES


hello and welcome to Auto inform online magazine how-to workshop my name is Frank massa and in this feature we’re going to demonstrate how to conduct diagnostic pin TAS at the PCM so within this module we’re going to demonstrate how to strip the socket how to use a multimeter and then compare those readings taking into account the entire circuit activity from the component back to the PCM so first of all I’d like to begin by stripping the socket the first part is and this particular socket design is increasingly now common so first of all there’s this cam arrangement which securely locates the pins now you also may notice the pins are very very small which is one of the problems now with Diagnostics is actually getting connectivity at the PCM accurately and of course the pin size is in the actual PCM are also quite small and the difficulty and the challenges to actually get the means of measuring across these pins without actually damaging the pins this particular vehicle has presented a very big challenge because the previous technicians actually damaged these pins we’ve had to toll twist splice the entire loom on every socket we’ve obtained second components and cut the loom and splice tips or a lot of work and we’re at the process now of testing the continuity from the socket to the component so first we need to do is remove this cam arrangement and there’s a couple of drive dogs which in the correct position allow off the cam to be removed there’s then a hood and there’s a strain relief tie wrap around there which I’ve previously removed we can then carefully let’s pull back a couple of little tabs and the hood slides off now the reason we’re doing this is well two reasons one we need to gain access behind like the cable and without actually intruding into the cable itself and we also need to examine the actual socket because these sockets have alphanumeric numbering in other words we have one two four and A through in this case I think 2g and you can see from this diagram the injectors are component y3 identified is the socket C which refers to the physical collection these Cu and now we can see that the actual pins relevant to each injector you can see that they’re alphanumeric and that of course refers to the physical properties of the socket once we’ve established that we can then begin our circuit testing so the first thing to do now and it’s important if we do in the type of testing we are now we’re basically measuring the resistance down the circuit that we must remove socket from the ECU the circuit needs to be unique and not attached to any other component functionality at all we have a multimeter and the first thing I’d like to do is you just check the reference I’m joining both cables together and just seeing what they the background value is so have point 2 ohms now what I’d like to do is I’m using the same probes by the way that we use with the oscilloscope these are all for male banana plug adapters for the tough interchangeable just remove that part of the probe attach the multimeter now before I begin testing here what I’d like to do is check the reference value actually at the component end the injector end that is the component only not taken into account in the wiring of course a wiring circuit is open at this end so I can now do a resistive check back at the injector and we’ll obtain a value so I want to connect back of the injector on each side of the coil and once again these probes will not intrude on the cable and we have an a stable reading 0.61 of an ohm and of course around point two of that is the value of the actual multimeter in the cable itself so 0.6 0.6 1 I would not anticipate any more than 0.3 point 4 of an ohm through the loom back to this end of the socket so we’ve already identified the alphanumeric reference for this particular injector and we now need to check that value back here at the PCM so we’re looking for around point six two possibilities we can go to the back of the cable so let’s just try connecting this side of the socket first now I’m showing you this way because there’s potentially a problem doing it this way one is that we may not actually connect on the back of a terminal and you can see from the reading there we are actually struggling to get down and don’t use too much force these pens are very small and the desperate we don’t want to damage there we have a reading 0.9 as a little bit more than I would have anticipated it’s stable so I’ll accept it none of the problem with probing in this way is that by going at the back of the pens there’s the possibility that corrosion exists between the cable and the pen before it actually makes contact with the ECU we have quite a high values 1.1 you can see that the value doesn’t vary considerably as I move those probes so you may get an inaccurate reading that’s one potential problem so let’s go to the other side of the socket so we’re dealing with Row 1 and Row 2 socket B now you can see we’re getting a lower value now I’m being careful not to push on the back of those pins too much these are quite fine probes that I’ve got and we have a value of 0.67 0.68 so we have a differential of point 0 7 which is acceptable so so far as continuity is concerned I’m happy that circuit has integrity it does not however prove a can carry current so do not confuse this test with a current test for the circuit this is purely continuity only and I’m happy to continue attack based on the process that we’ve used that this circuit is good now of course the proof of whether circuit can carry load of course is that there must be alone but at least that test is confirmed that we do have a good circuit between the PM socket and the injector you could also use this method for wiggle testing wiggle testing is where you may think you’ve got an intermittent break in the loom provided the probes are in and secure and you may want to have somebody actually hold them providing the they are secure whilst you exercise and wiggle the loom to see if you get a variation in the reading there are some difficulties with that of course because quite often and this vehicle is a good example of this the loom really has a quite a torturous route between here and the engine the components anyway which is really why most of our testing now is done accurately ECU where as you can see accessibility’s more favorable we have of course cut back some of the taping on the loom for two reasons identifying the wires by color and as I suggested earlier so we can actually maneuver the cables into a position where the probe can be inserted carefully alongside the cable down hopefully to the back of the pin so the critical components are very fine at strong but sharp durable needles and direct access into the back of the cables and of course the schematics of the wiring are important so we can identify the alphanumeric coding of the socket that concludes the how-to workshop and I hope to see you in the next feature you


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