Unlike MOSFETs, old school Bipolar Junction Transistors (BJTs) have a ~0.7V voltage drop across them. Not surprised to see them being used for relay control in an 1998 car. Even if you have 0.7V drop, it is still >11V across the relay coil, more than enough to turn it on... if the relay is good, of course!
I went through something similar on a BMW. It turned out to be a faulty fuse. But not that it was blown. But that it had high resistance. And was causing a voltage drop. If you unplugged the i.a.c. it would start and run. Took me a while to figure that one out. But in truth it was one of Mario's videos that gave me the tools. I'd learned to load test circuits instead of just assuming power is good just because the fuse showed power. So when I load tested the power going to the i.a.c. I saw the voltage drop. And the power going to the i.a.c. was also the main relay power. So the fuse was good enough to handle only the load of the relay. But not both the relay and i.a.c. Lesson learned.
I have a no crank on my 2000 750,I only replaced the top battery thinking I would get something but no I’m getting full power in the cock pit,but no crank
Being a technician myself with the background in aviation having repaired various fighter jet systems and attack helicopters, I can appreciate your diagnostic delivery and instruction. So many need the skill and advice you and others like you give and impart to make their problems solvable. I especially like your delivery and straight forward way of showing the connection between the cause and effect. Your equipment is top notch too and mt Xtools D7 box although good pales in comparison to yours😅 I gotta get me one of those. Thanks again bro for the lesson and the quality technician that you are. Keep the spark going.😊
I had a similar issue with my E38 740il, no crank and no start but I could hear a click noise. INPA indicates low voltage in the EWS - Code 148 error. I opened the E-box and wiggle the starter relay K6324 voila - the car fires up straight away. I note you've replaced the DME relay K6300, did you replace the starter relay as well? What was your customer's symptoms? Did the car able to crank at all?
I think I’m having same issue with my 98 740 il no start no crank but I definitely hear a click each time should I try to wiggle the starter relay as well ?
Great video and straight to the point. These videos are short and sweet but hold so much diagnostic info to help keep us from chasing our tails. Thanks Rio!!
As to the 0.7 V, that means there still would be at least 11.3 V over the relay coil. A 12 V relay should activate at no more than 80% of the label value, in this case at most 9.6 V. Two of the common problems on these kinds of relays would be open coil or some mechanical issue like dirt. With open coil, you would not get any current and never see the 12 V and 0.7 V readings combination at the low side. So, I would suspect a mechanical issue. Dirt in the magnetic path. Or a slipped hinge structure. I have seen both kinds -- not on cars, as I am not dealing with them. But relays in other applications.
Great video, I was a BMW tech back in this era of BMW, it brought back memories of doing similar tasks. Today I'm a DIY'er. On more modern stuff I try to research how to test a sensor or in the case of the fuel pump before replacing. I encourage anyone who is a DIY person to slow down, research forums and or youtube then do some testing of components in question instead of throwing parts at it. The money saved can buy you some more professional tools or a higher end scan tool . Mario, I could watch your videos all day long!
Great video Mario.. not for nothing but I’m glad your motorcycle broke and you didn’t just take it to someone to fix it. Haha God bless brother. Always appreciate you. Love keeping it basic when you can!
My 750 E-38 is getting no start,but turns over,2-new batteries,please,what’s my first step,fuel pump comes on,,it acted like it wants to when i sprayed into the two filters
Changing fuel pump without disconnecting it and checking it with a 12v external battery ? Why did customer change sensor ? Why did the relay stop working ? Book in the trunk is not cutting it. Watched with great pleasure.
HI. I HAVE THE SAME CAR 740I E38 1996 V8. I DROVE THE CAR MANY TIMES WITH NO PROBLEMS. 1 EVENING I PARKED IT. OPENED THE BONNET TO CHECK WATER AND OIL. 10 MIN LATER TRIED TO START TO PARK IT IN THE GARAGE. NO CRANK NO START. LEFT IT AS IS WITH THE KEY INSIDE. NEXT DAY THE CAR HAD LOCKED ITSELF WITH THE KEY IN IGNITION. AFTER A LONG HANGER WIRE IT OPENED. NOW IT CRANCKS BUT NO START. PLEASE HELP
Same thing is happening to mine. I bought this hoping to restore. My first restore. You can imagine how delusional I was thinking I could do it easy. It's looking good but this crank no start is killing me. I don't have a big budget for this right now so I'm hoping what you did will fix the issue. Thank you for this.
Great catch mario. Those 740 are pretty nice we don’t get many in Boston in the show they slip and disengaged dead in the water lol. One of my favorite cars tho
You still holding back knowledge brother and I never disagree for paying to learn but when one is starting they need all the support system that can accelerate their carrier , I guess every trade will hold a bit and I have seen many times , thanks for sharing your knowledge Mario cheers
