1998 740i Trans Fail Safe Mode and Codes

[PlsBear85]

I have the trans safe mode occurring, starts off very slowly and doesn't start driving smoother until about 25-30 mph. Car can't really get past 2000 RPM's while driving. It can rev up pretty high though. The car is an automatic, has 170,000 miles on it. Also has codes for Speed Sensor P0500(I believe this is associated with the wheel speed sensors, the ABS light is on also. Which makes me think this is part of the main issue, the transmission needs that information to operate). As well as Speed Sensor Circuit P0720(I can't figure this one out, not sure what it is referring to). And Gear 4 incorrect Ratio(Thinking low fluid or dirty fluid. I know it can also be a solenoid or actual mechanical issue). My battery is also bad, I had it tested and it came back as running at half of what it should be outputting. I figure the alternator could be issue, I need to check the voltage on that. The car works in every gear, shifts to every gear. I am thinking this is mostly electrical. I am taking it in to have the codes diagnosed, to see the cause of the issue. I may replace the battery first, which is $170, and see what happens. I had thought of doing a transmission oil change and filter change, as well as sensors. Not sure where to start exactly... Any advice or insight is useful. Maybe someone has this issue and the same codes are coming back. It does not feel mechanical, but who knows. I love BMW's, I love fixing them and selling them so I can get a different one. I love this one though, something special about it. And it's my first V8. I am stumped though, this is a first time for me with this issue. Thank you for taking the time to read and hopefully respond.

[srq]

A lot of problems and fault codes could be related to low voltage. I would start w/checking the charging voltage from the alternator. You should get 13.5 - 14.0 volts. If voltage checks out OK while car is running, check the battery. Take battery to Battery Surplus and they can load test it to see if it is holding charge.

[mooll]

sorry , but your trans is gone
p0720 is death code to e38 trans

[PlsBear85]

I am having the alternator tested today, I believe this is very much an electrical problem causing the main issue. Maybe not, but I do not believe it is the death code. The fact the wheel sensors are bad, is huge. The battery is in bad state. I'm not the type of person to just get a new transmission because someone tells me they think it's dead. There are obvious signs that fixing the other codes, can very well fix the issue. I may need an output sensor as well. If I need a torque converter, they only go for $200. I will keep you updated, again, any positive feedback is much appreciated.

[mooll]

I am having the alternator tested today, I believe this is very much an electrical problem causing the main issue. Maybe not, but I do not believe it is the death code. The fact the wheel sensors are bad, is huge. The battery is in bad state. I'm not the type of person to just get a new transmission because someone tells me they think it's dead. There are obvious signs that fixing the other codes, can very well fix the issue. I may need an output sensor as well. If I need a torque converter, they only go for $200. I will keep you updated, again, any positive feedback is much appreciated.

lol i'm not telling you to go out and buy a new trans that was just my .02..
when i got that code my trans was bad and same with one other members' trans recently and if you search p0720 usually means blown clutch or A- drum or something not good. i do understand your alt may be bad though so good luck there !

[PlsBear85]

Mine is an Auto, so no clutch issues. It just doesn't feel mechanical, but who knows. The alternator is performing below what it should be. So I will replace the alternator and battery first. Then I am going to diagnose the ABS wheel sensors, as well as diagnose the speed sensor and see it it is a sensor on the transmission. Or if it is the abs sensors themselves. From there, need to a transmission fluid change and filter. I'm pretty much starting from the ground up. Hoping to get it fixed. And not you, but others told me its the transmission, without even looking at it. That's what I get for going to a "Bmw" specialist. I own a bmw, but I'm not bmw rich.

[whiskychaser]

A quick look at the codes suggests road speed sensor and trans output speed sensor problems. It is worth remembering that the code refers to a fault with the circuit. So don't automatically assume that replacing them will fix the problem. There are tests you can do before you bin them. Ensuring you have enough voltage to run the TCM is a great place to start.

[PlsBear85]

Yeah that is what I have been trying to figure out, what is the "circuit" exactly and where? I had a feeling about the output sensor, it just makes sense. I know the shotty alternator and bad battery are not helping to give power to the units. Those two things going, I wonder, if they caused the other issues I'm having partially. I don't have all the appropriate tools to do full on diagnostic, so I will be taking it to someone to have them check the codes and get to the root of the problem. They said they would only charge me $90, so I can live with that. I do want to have everything electrical checked and fixed before I start doing a transmission filter change and oil. Thanks for the advice.

[Timm]

The output speed sensor error means that the EGS (gearbox computer) has selected a gear, the input shaft to the gearbox is turning (driven by the torque converter), but the output shaft isn't. This fault is generally seen when one of the clutches have failed and the only forward gear available is 4th/5th. The usual behaviour is that you put the car into Drive, there is a bit of a bonk as the EGS notices the turbine is turning and goes into emergency mode - TRANS FAILSAFE appears on the dash - and then you will notice the gear indicator on the instrument cluster goes blank and that you have very little acceleration (due to being in 4th gear).

This is all normal stuff for a clutch failure except you say the gearbox works fine in every gear, what do you mean by that? Can you see the gears selected on the instrument cluster?

[PlsBear85]

I suppose I mean that I can put it into each gear and it won't slip out of it. I can see the gear changes. Unfortunately I can't see my on dash very well. I think that is from the alternator and battery going bad. I changed out the fuses for them already. the car will drive up 60-70. No noticeable noises or shakes. I don't drive it that fast currently, but I had to see if it could. Will replacing my output speed sensor possibly help solve this problem?

[mooll]

Mine is an Auto, so no clutch issues. It just doesn't feel mechanical, but who knows. The alternator is performing below what it should be. So I will replace the alternator and battery first. Then I am going to diagnose the ABS wheel sensors, as well as diagnose the speed sensor and see it it is a sensor on the transmission. Or if it is the abs sensors themselves. From there, need to a transmission fluid change and filter. I'm pretty much starting from the ground up. Hoping to get it fixed. And not you, but others told me its the transmission, without even looking at it. That's what I get for going to a "Bmw" specialist. I own a bmw, but I'm not bmw rich.

well enjoy wasting hundreds and hundreds of $ more on things you don't need...
guarantee replacing those sensors will do nothing and they not exactly cheap.
when you do the fluid/filter change check the pan for metal bits/pieces/shavings, then you'll know for sure.

[PlsBear85]

The magnets collect those things naturally, that's why they are there. It's not wasting money, and those parts are not that expensive. And it is work I can do myself. Replacing those sensors will make a difference, the transmission needs them to be in good working order. Other wise, your car goes into trans fail safe mode. One of the most expensive repairs will actually be the alternator and battery. Though if a person knows where to go, things aren't so bad. When it's a BMW, it's never a waste of money. Figured you would know that

[whiskychaser]

As Timm says, the TCM monitors the input and output speed sensors. In simple terms, it thinks you are pedalling your bike and getting nowhere. Now that could indeed be because the chain came off. But it could also be because you don't have the correct voltage to run the sensors. So start by sorting your voltage issue and work from there.

[Sean faddis]

Not starting

[Vaughan Mills]

I have the trans safe mode occurring, starts off very slowly and doesn't start driving smoother until about 25-30 mph. Car can't really get past 2000 RPM's while driving. It can rev up pretty high though. The car is an automatic, has 170,000 miles on it. Also has codes for Speed Sensor P0500(I believe this is associated with the wheel speed sensors, the ABS light is on also. Which makes me think this is part of the main issue, the transmission needs that information to operate). As well as Speed Sensor Circuit P0720(I can't figure this one out, not sure what it is referring to). And Gear 4 incorrect Ratio(Thinking low fluid or dirty fluid. I know it can also be a solenoid or actual mechanical issue). My battery is also bad, I had it tested and it came back as running at half of what it should be outputting. I figure the alternator could be issue, I need to check the voltage on that. The car works in every gear, shifts to every gear. I am thinking this is mostly electrical. I am taking it in to have the codes diagnosed, to see the cause of the issue. I may replace the battery first, which is $170, and see what happens. I had thought of doing a transmission oil change and filter change, as well as sensors. Not sure where to start exactly... Any advice or insight is useful. Maybe someone has this issue and the same codes are coming back. It does not feel mechanical, but who knows. I love BMW's, I love fixing them and selling them so I can get a different one. I love this one though, something special about it. And it's my first V8. I am stumped though, this is a first time for me with this issue. Thank you for taking the time to read and hopefully respond.

Were you ever able to fix this?? I’m having almost the exact same issue. I have a wheel speed sensor engine code along with all the abs lights. My trans failsafe light just came on this morning. I just replaced the battery today and it didn’t fix it. My alternator is working properly so that’s not the issue. I love this car so much and I want to get it fixed ASAP since it’s my daily. Thanks in advance

[Vaughan Mills]

Were you ever able to fix this?? I’m having almost the exact same issue. I have a wheel speed sensor engine code along with all the abs lights. My trans failsafe light just came on this morning. I just replaced the battery today and it didn’t fix it. My alternator is working properly so that’s not the issue. I love this car so much and I want to get it fixed ASAP since it’s my daily. Thanks in advance

[tylamb19]

Were you ever able to fix this?? I’m having almost the exact same issue. I have a wheel speed sensor engine code along with all the abs lights. My trans failsafe light just came on this morning. I just replaced the battery today and it didn’t fix it. My alternator is working properly so that’s not the issue. I love this car so much and I want to get it fixed ASAP since it’s my daily. Thanks in advance

Have you scanned EGS (transmission computer) for codes? Trans fail safe will set a code in the EGS, that should point you in the right direction.