mercedes no crank (when Hot)

[Music] hi everyone and welcome back to a new episode of diagnose dan today we are working on a 2007 mercedes 280 e-class and the customer complaint is that the engine won't crank or to be more specific it won't crank when the engine is hot as long as this car is cold it cranks every time but as soon as the engine has warmed up it refuses to crank so let's diagnose this mercedes together [Music] the only thing i did so far is remove some of these plastic covers now this engine is cold right now i can't even touch the exhaust the customer told me that when this engine is cold it always cranks but as soon as the engine heats up it refuses to crank now to confirm we don't have a problem when this engine is cold in the next step i'm going to crank this engine five times [Music] as you could see absolutely no problem when this engine is cold just like the customer told us now to confirm we do have a problem when this engine is hot we need to run this engine to allow it to get up to operating temperature and after that we're going to crank it again the engine has warmed up and according to the customer every time the engine is hot it won't crank anymore until the engine has cooled down again so let's see what happens let's try again and that's customer complaint confirmed the customer is absolutely right this mercedes does not crank when the engine is hot now there are many things that could prevent this engine from cranking i mean there's the immobilizer ignition switch starter motor starter motor relay park neutral switch brake light switch i mean there's too many things i wouldn't know where to start so in the next step we're gonna scan the car for codes and hopefully there's something in there that gives us a clue where to start our diagnostics i did a full system scan and most systems came up with no fault codes now there is a fault code stored in the engine computer and i was kind of expecting this because the check engine light is on but that fault code is for an inlet camshaft solenoid and i'm pretty sure that won't prevent this car from cranking now there are other fault codes stored in the abs in a door module and in a mobile phone adapter but i'm also pretty sure that's not what's causing our no crank almost all systems pass without any fault codes we do have got a fault code stored in the engine computer for a camshaft solenoid in a door module for a heated mirror in a phone adapter for a microphone and there is a history code in the abs for low voltage on a solenoid but none of these codes should prevent this engine from cranking now where should we start now don't panic we're gonna start out by doing some basic checks a we're gonna see if the starter motor cranks when we try to operate it manually to rule out we don't simply have a bad starter motor that fails when it heats up from the engine need b we're going to check if there's a starter motor command now both these things can easily be checked at the starter motor relay to find the starter motor relay we have to take a look at service data in this case the starter motor relay is conveniently placed right there [Applause] now this is the underhood fuse box and when we take a look at the picture i found in auto data this should be our starter motor relay l as you can see it's located right next to that big 40 amp fuse now from here we should be able to manually operate the starter motor when we take a closer look at the starter motor relay we can see on this relay like on most relays there's a schematic which is very convenient when we take a closer look to the schematics on the relay we can learn that the control side is between pin 1 and 2. the switch is between pin 3 and 5. i took a look at the wiring diagram and i've learned that pin 5 should be a power and when the switch closes that power can flow from pin 5 to pin 3 and activate the starter motor we should be able to manually activate the starter motor by applying a power to pin 3 which is this pin in the fuse box when i apply power with my power probe to pin 3 in theory that starter motor should crank now i quickly reinstalled the starter motor relay moments ago to check if our problem is still there because we gotta take into account while we are diagnosing this car this car is cooling down now it didn't start so if it does start by applying a voltage to pin 3 we can rule out the starter motor being our problem so the starter motor is not our issue so in the next step we're going to take a look at the control side of the relay the ignition is turned on and when the ignition is on there should be power on pin one of the relay now according to the relay this should be pin one so that should be this pin in the fuse box now when i hook up my test light to ground and i touch that pin the test light should light up and it does so there is power on pin one of the relay so right next to pin one there is pin two and i'm going to put this little connector in pin two and i've got my test light hooked up to battery positive so when i touch a ground the test light should light up and it does now pin two should be a switch round when we attempt to crank the engine so when i put my test light in that connector and i attempt to crank the engine the test light should light up so attempting to crank the engine right now there we go and cranking and cranking and as you can see the test light does not light up so somehow this relay is not being controlled as you could see the starter motor relay is not being controlled and if the starter motor relay is not being controlled of course the starter motor is never going to crank now the big question is why is the starter motor relay no longer being controlled when the car reaches its operating temperature in the next step i want to take a closer look at the electronic ignition switch which is a part of the car's immobilizer system i want to use the scan tool to take a look at scan data before we do so we need to understand two things terminal 15 is the key on position so when i turn the ignition on terminal 15 should change from off to on terminal 50 is the crank position so when i attempt to crank the engine terminal 50 should change from off to on if it does so in theory this car should crank right now we're in the scan data for the electronic ignition switch we can see there is no key in the ignition switch and both terminal 15s are off terminal 50 which is the crank position is also off now let's put the key in the ignition switch and turn the ignition on right now we can see that there is a key in the ignition switch and both terminal 15s are on of course terminal 50 is still off now let's attempt to crank the engine we can see that terminal 50 changes from off to on so in theory this car should crank so we got no relevant fault code stored we've got a cranking signal coming from the ignition switch the starter motor is good the starter relay is good but we've got no control when it's hot really this car should crank now i took a cup of coffee and parked the car in this part of my shop to let it cool down for an hour to show you guys that when it's cooled down we no longer have a problem now of course when the starter motor is cranking the starter motor relay is being controlled now to show you what that looks like i'm going to remove the relay put my little connector into the control pin of the relay and this relay is ground side switched so i'm going to hook up my test light to battery positive and when i crank the engine of course the test light should light up and as you can see it does so absolutely no problems when the car is cooled down now let's take a look at a wiring diagram the diagram tells us that the ignition switch is not directly in control of the starter motor relay instead it puts the crank command on the can bus it then runs through a can bus connector and it's then being received by the engine computer the engine computer is the one directly in control of the starter motor relay so that signal is coming from the engine computer and not from the ignition switch now which of the components in the diagram could actually heat up could it be the ignition switch well i don't think so it's placed inside the cabin and inside the cabin it doesn't really get very hot but after looking at this diagram i did get suspicious about one particular component and that's because of its awkward location because on this car the engine computer is placed directly on top of the engine and an engine gets hot so my theory is when the engine eats up it heats up the computer and when the computer is hot it no longer controls the starter motor relay now on closer inspection my suspicion actually got stronger because it looks like in the past this computer has already been repaired [Applause] so to test my theory i'm gonna take this heat gun and heat up the computer and only the computer nothing else so i'm gonna heat up the computer attempt to crank the engine heat it up crank the engine heat it up crank it until hopefully at some point the engine will stop cranking and my theory is confirmed [Music] hmm oh foreign [Music] so and no longer cranks as you can see the only thing that is hot is my heat gun and the engine computer now although i'm pretty sure we found a problem we need to be thorough so i'm going to do a continuity and a resistance check between the control pin of the relay and the pin in the connector of the computer now i think it's this pin over here and it is and we've got 0.2 of an ohm 0.1.2 of an ohm so that's perfect next i'm gonna do a wiggle test and if something's wrong we're gonna lose that beep and there's nothing wrong with a wiring harness so i'm going to do one less thing i'm going to do a pin drag test and if that turns out to be fine i'm gonna call it a bad computer i opened the computer and i could definitely see someone had been in there before because the ceiling they used was definitely not how it left the factory and actually i had a very hard time opening it i did a quick visual and i could see nothing obviously wrong with it now i could do some more testing but i had a talk with the owner of the car which is a very nice lady and she told me dan this is an old computer it's been repaired before if we're going to repair it again what's going to fill next please order a new one and told her this is not going to be cheap she says i know but i need this car to be reliable for my job so please do so i kind of think she's got a point so i'm going to order a new one and once it comes in all we need to do is program it and this car should be fixed [Music] so [Music] [Music] so [Music] [Music] after the repair the customer picked up the car and she's been driving for quite some time now and she told me that the car cranks every time even when the engine is hot now a lot of people think that diagnosing a car is just stopping by a shop hooking it up to a scan tool and read the fault codes now this video is a classic example that this is absolutely not the case i mean there is no fault code b10000 when the engine heats up the engine computer no longer controls the starter motor relay it's just not how it works now lately i've been getting a lot of questions if there is an automotive textbook that i can recommend now the latest book i've been reading is this book written by tom denton thomas has been writing best-selling automotive textbooks for over 25 years and i have had the privilege to be a small part in his latest edition so if you want to become a skilled diagnotician please take a look at one of tom's books now i really hope you enjoyed this video if you did please subscribe to my channel and when you hit the little bell you'll get a notification each time i upload a new video and remember diagnosed then fix it again see you next time guys you

Channel: DiagnoseDan

Views: 146,385

Rating: 4.9681253 out of 5

Keywords: Mercedes, no crank, im608, autel, South main auto, die autodoktoren, scotty kilmer, hoovies garage, scannerdanner, Bosch 9.7, w211, startermotor

Id: vl9U_pQzKfo

Length: 19min 54sec (1194 seconds)

Published: Mon Oct 26 2020