You know , really , what could this be ? On prior posts , it has been determined that I have no battery or alternator issues . At start up only do I very occasionally get the flashing m and s with blinking gear selector , with corresponding "limp" mode . Then when that happens , the engine is turned off . Then restarted and its like nothing has happened . I don't get it ? If something was loose , then these actions would apply just driving around . But only at start up . Bad relay ? And why so infrequently ?? XYZ switch ? Computer ? Elves ?

 

I've been here chasing the same issue in the past. Chased it for months. The main issue I had was bad battery terminals especially the ground. I could tighten them but still would have movement. Scraped the terminals for Mil-Specs. I also upgraded the Big 3 with 1/0 cables/lugs. I run a fridge and other stuff so made sense. The main ground at the shock tower was redone. Cleaned all the grounds. Check all connections at starter/Alt and grounds. This solved my issue and has not returned. Before this fun project I had the M+S appear once and found the small ALT wire from the harness had frayed. It was barley hanging on. I spliced a new wire on to connect to the back of the ALT and solved the issue.

I know you said the battery is good but did you have it tested under load? It could be loosing enough charge to trip the M+S. Then after restarting it the system is good? I had a run of crappy batteries from a Big Auto Store. They would only last 2yrs. The last time I just scrapped it and picked up an X2 battery. It's been 3+yrs on this one. I posted in your other thread about a battery tester I picked up on AMZN that reads the health of battery and can test it under load in or out of truck. Best of luck.

 

Thanks, Windy , I will clean my grounds . But what is odd , is that after restarting , it works fine . If it was a ground issue , wouldn't the flashing lights occur during driving ?? Why at start up ??

 

The starter is the biggest single draw on the battery. At startup, the battery sees max stress and the voltage drops. Once the truck is started the alternator kicks in and the voltage is largely stabilized. I don't know if this is your issue, but it is a very common cause of issues at startup.

 

I had this exact same issue just a few weeks ago. My 18 yo daughter is driving my Disco at the moment and I didn't want her stranded somewhere with a dead battery in the middle of New England winter, so I just threw a new battery at it. The symptoms went away for a few days, but then came back exactly the same.

I figured hmmm, must be the alternator, so I went and grabbed the ready one from the basement. When I went to disconnect the battery to change the alternator I found that the ground wire was loose enough that I had to hold it steady in order to back off the tightening nut. This made me realize that I potentially had a connection issue, and it's then that I remembered that a couple of days earlier when I was driving I had noticed that the static in the radio would increase whenever I was pressing the brake pedal (and the brake lights were lit). Together these two things made me realize it was a grounding issue.

It is pretty cold here in CT these days and I didn't feel like spending an hour or more replacing the leads or connectors right this minute, so I bought some of the cheapo battery shims down at the auto parts store. Fixed the issue immediately and haven't had any other issues since. Once the weather gets a little warmer I will take the time to fix with a more permanent solution.

 

The M+S is a strange one for sure....Initially at start up I would think that surge exposes a ground connection as faulty/loose. That first surge may be enough to reestablish the connection even though it is faulty/loose. Turn it off and back on the system accepts it the second time?? I will say when I was chasing this M+S issue it always occurred during rainy/cool weather. Sometimes at initial start up and limp mode. Other times while driving and enter limp mode. Mid 30-40s temps and rainy. When I discovered the connections being loose I could literally pop the neg off the terminal with very little force. The positive I could twist a little. Didn't matter how much I torqued the connections they would still move.

After my post yesterday I remembered a M+S issue just a few months ago. I had the truck raised while changing sway bar bushings. Left it raised over night. Finish job next day and drop her down. Go to fire her up and it doesn't start. Wait a sec and try again. Fires up but M+S come on. Check terminal and they are tight. Kill engine. Start it up again. Starts normal. No lights. I write it off since I had the truck jacked up in different angles and left it all night. Next day truck starts fine. No lights. Drive 5 minutes and get on highway. Truck cuts out for a split second. Very strange......drive another 10 minutes and loose all power. Truck dies on highway going 65mph. Get towed home and determine my CKPS took a dump. My only warning was a failed start once and a M+S. Replaced CKPS and back in business. It was the original and I had 196K at the time.

I know from reading tons of threads about the M+S issue on various forums it usually involves a electrical connection issue. I'm not trying to muddy the water with the CKPS but simply sharing my experience with it. That's one of those failures with no code at least in my experience. Good luck!

 

Likely an xyz switch issue. If you have the blinking D on the dash and blinking light on the shifter, that means the car is having an issue determining what gear it is in. If there is a small bit of corrosion that messes up the contacts sometimes, the car will be in limp mode and start flashing once it detects something is not right. Even if it starts working again, you might still be in limp mode. I had a similar issue and kept getting the flashing m+s more often. I took apart and cleaned the xyz switch, but it still flashed upon installation. Once I cleared the codes to make the computer forget it was in limp mode, it has worked, and the flashing did not come back. I would scan the codes and see if you have P0705. If you do, the XYZ switch is the issue and needs to be cleaned.

 

It's worth saying again because it's the cause 100% of the time in my experience - make sure your battery is charged up and topped off. For reference, I charge my battery every month just as a maintenance item and almost always it takes 30-20%.