Picture this: you are driving along when, out of the blue, your car’s transmission starts acting up. The “check engine” light comes on, telling you that there is a problem. At the same time, your car’s transmission automatically shifts into second or third gear and stays there.
What Transmission Do I Have?
Limited to one gear and 30-45 mph, you know there is a serious problem with your car’s transmission and you have to get your car to either your dealer or transmission repair shop to have the problem diagnosed and repaired.
Naturally, the first questions that go through your head are: Why did this happen? How severe is it? and How much will it cost to fix?
In This Guide
- What Causes Limp Mode?
- Limp Mode’s Protective Actions
- Example Situation
- How the Computer Determines That a Sensor is Incorrect
- What You Should Do
- Questions to Ask Yourself
What Causes Limp Mode?
Today, nearly every system in your vehicle is operated by the computer – including the transmission’s line pressure, shift timing, sequence and feel. The vehicle speed sensor provides input to help control ABS, fuel mixture, fuel injection and transmission operation. The manifold absolute pressure (MAP) sensor and throttle position sensor (TPS) provide the engine’s load information which is used to manage the shift and downshifting in the transmission when you’re driving up an incline or you’ve put the pedal to the metal.
Fail Code conditions or “Limp Mode” occurs when there is a problem with the logic of a vehicle’s computer. When the signal value sent by a sensor to the computer is not within a pre-programmed range specified by the manufacturer, it will switch to “secondary” programming. These procedures are designed to protect the transmission from further damage that could be caused by the signal error.
As long as the computer is receiving signals from the MAP, TPS, vehicle speed and other sensors that fall within their “normal” ranges based on the current conditions, the transmission will operate normally. However, as mentioned above, if it receives a signal that is outside of the expected range, it will switch to secondary/emergency operation.
The exact measures taken in secondary operation is determined by the computer’s logic as programmed by the manufacturer and depends on how far outside the acceptable range the signal is (if there is any signal at all). It might react differently when the value is higher than the highest parameter than it does when the value is lower than the lowest allowable value.
Limp Mode’s Protective Actions
If the signal value wasn’t far enough outside of the range to indicate a mechanical failure, the first thing the computer will do is turn the check engine light on to alert the driver that they should have the vehicle checked out using a code reader/diagnostic scanner to see if there are any “soft codes” listed. Soft codes can indicate that a low priority sensor has malfunctioned or is starting to break down. If the light goes away after restarting your car, it could mean that the sensor only failed once due to a loose connection or it could be a sign that its condition is getting worse. Critical functionality is typically unaffected by this kind of problem, but if the issue isn’t resolved, it can negatively impact the performance or fuel efficiency of the vehicle.
Now, if the signal value from a high priority sensor (necessary for critical functions) is dangerously far out of the acceptable operating range, the computer switches over to secondary “survival” mode. This is known as a “hard code”. In this mode, the computer shuts off the electronic shift solenoids. This disables the transmission’s ability to shift gears and causes it to default to single usable gear – usually second or third. In addition, the pressure in the transmission’s fluid lines is set to high in order to protect the bands and clutches from being damaged. The signals that control the line pressure are set to “full on” to prevent the clutch pack from a slipping dangerously.
All of these changes result in the previously described “Limp Mode”. Instead of leaving you stranded with a broken down vehicle, it enables the vehicle to limp home or to the nearest service center for repairs while reducing the risk of doing further damage.
Example
For example, one of situations that would cause a transmission to go into limp mode is if the cable harness going to the transmission is damaged or detached. In this case, the computer would sense that it lost communication with the transmission, but since the harness is detached, the command to go into limp mode cannot make it to the transmission. However, with no power supplied to the solenoids, the line pressure is set to high and the transmission is stuck in 2nd or 3rd gear – the same effect the limp mode command would have.
How the Computer Determines That a Sensor is Incorrect
Say, for example, that the computer receives a signal from the Throttle Position Sensor (TPS) stating that the pedal is to the metal when the throttle is actually closed. It would spot this error when it compared this status with the vehicle speed sensor, which would be signaling low or no speed. As soon as it sees this discrepancy, the computer will command the transmission to go into limp mode and turn the check engine light on. A signal value by itself can’t always be classified as an error, but when analyzed with other sensor outputs, the computer can easily figure out if there is a problem.
The fault code of the sensor causing the error is recorded by the computer. A mechanic can use a diagnostic scanner or code reader to find the recorded codes and then look them up in a table from the manufacturer to determine which sensor, and therefore which system is the source of the malfunction. Many scanners are pre-programmed with these tables and return more information than just the codes.
For example, the diagnostic scanner could return the code “35”, which indicates that the problem has to do with the transmission fluid temperature sensor. The abnormal values that were recorded and the “normal” range for the sensor could also be provided to the mechanic.
It is recommended to have a vehicle’s computer scanned regularly for fault codes – especially if the check engine light is on. This is done by most service centers during routine tune-ups.
What You Should Do
If your transmission is in limp mode, your transmission has a problem and you should get it fixed as soon as possible. Here is what you should do:
- Do not panic! Limp mode is specifically designed to limit further damage and allow you to get your car to a service center
- If possible, drive directly to a service center
- Otherwise, drive home and call a service center to have your vehicle towed
- If you do not feel comfortable driving at a limited speed, pull off the road where it is safe to do so and call for a tow
- It is advised that you do not continue to drive a vehicle in limp mode as it is unsafe and can cause further damage to your vehicle
Questions to Ask Yourself
Once your vehicle is safely in the service area, it is time to answer a few questions that will help diagnose the problem:
What Transmission Do I Have?
- How fast were you driving and how long had you been driving when the problem occurred?
- Did any lights on the dash come on? Did they come on when you started the car or after driving a while? Did they stay on?
- What repairs or maintenance has been done to the vehicle in the last month?
- Have you noticed any signs of a problem recently (noises, behaviors, leaks, etc.)?
More Information by Transmission Type
Problems by Make & Model
OBD2 Transmission Trouble Codes
| DTC Code |
|---|
| P0218 |
| P0702 |
| P0705 |
| P0730 |
| P0740 |
Bought a 2009 Jeep Patriot. Had the transmission replaced with one that had 133,000 miles on it. about 2 years ago cause the transmission was shot that was in it. Now it has gone into limp mode 3 times. It has 201,360 for miles. Everything else is great on it.
I have a 2012 Cadillac CTS4 all wheel drive. The car will periodically go into limp mode. When this occurs I stop, place the car in park and restart it. This clears the issue and car runs normal. Problem is I’m afraid to go anywhere for fear of a total breakdown.
Hi
I have a Peugeot 308 with AL4 gearbox, it does not power the wheels unless I high rev it.
On scanning, I have the error P0721 speed data fault. Also gearbox fault on dash. The code is from the manufacturers software Lexia/diagbox. This gearbox does not take the output speed from the gearbox instead it uses the ABS speed sensors. I have changed transmission oil and cleaned the valve body, but cannot resolve the issue. I notice the gear activated is 1 in Drive initially and then will move to safety 3rd refuge when I keep revving. I noticed oil pressure difference is more than 50 percent compared to the guide pressure and this can be seen in the fault variables pic.
Ford E-150
transmission will not go in gear or shift unless check engine light is on & overdrive light flashing 1996 F350 powerstroke automatic transmission
i have a 2006 ford freestyle and it wont start . everything works but it shut down on me and ever since its been on limp mode just want my car fixed
I have a 2017 Chevy Silverado 2500hd first I had a problem with the fuse box got it replaced with a new one and after that’s when I started having issues wth the transmission works great in reverse but on drive sometime it catches and then it doesn’t and when it don’t I give it a little gas and it catches sometimes and it tends to rev up when I give it gas while it’s trying to catch in gear.
Well I am having tranmison problems
Why does my 2003 accord sometimes while driving the d4 on dash starts blinking, I have to stop , turn off car then start it again?
I have a 2010 Chevrolet Silverado 1500 just rebuilt the transmission put back in and now it wont move so then was told it was my torque converter so went and got another 1 put it in with another new filter and fluid and it still wont move now am told that it could be in limp mode or the valve body needs to be reprogrammed I dont know what’s goin on please help
I have a 96 Explorer that just came out of the tranny shop. (reason was it was going into limp mode) They assured me that it ran fine after the repairs. (over $1700.00)
Was able to drive home, on Friday but Saturday – it went back into limp mode.
I had a brand new PCM, (preflashed), that I put in at home on Sunday. Car started fine. Went through all the gears slowly – still fine. Went for short test drive, (less than a block), and the problem occurred again.
I now suspect one of the many sensors may have been causing the problem all along, but without a code reader, I’m up that proverbial creek without a paddle.
Monday…Called the transmission shop and the owner advised me to tow it back in – to make sure it wasn’t something they overlooked.
I cannot afford to pay much more to them when it may in fact be only a faulty sensor.
HELP
what did the tranny shop fix
Have 2016 Ford Fiesta. Bought New from Ford Dealership in 2016… Car Now Has 6,000 miles on it. Battery died. Charged it. Engine light and Transmission Malfunction lights came on. Drives perfect,but can’t get lights to go off
Im driving Mercedes c180, and nou it does not change or move, but i switch it off, when i start it it shows engine light n the is a sound on the gearbox, what could be?
How can I reset my car out of limp mode
Disconnect and reconnect positive terminal on battery
i have a 2015 focus and i drove it without the hood on or the cover for under neath the motor and trans. needless to say it sat also and my starter went out. i replaced it and it started right up. bout the third or fourth time i let it run for about 10-15 mins. i shut it off and when i went to restart it agaqin, nothing. i looked underneath and saw that waqter was coming from the bell housing right where the starter bolted on. i figured it got shorted out. i bought a new but b4 installing it, i loosened the bolts holding the trans to the motor on the bottom side and one or two on each side of the trans.it probably let mecrack the bottom side of the trans maybe at the most without forcing it close to an 8th of an inch. just enough to get a drip going to drain the water from inside. i left it up on stands (the front end only) for bout 2 weeks with a drop light close to it to help evaporate the water. now when i get in the car theres a lot more clicking from this piece on the front side of the trans and my car will start but will not engage into any gear. i can shift from park all the way to low and it will not engage. im pretty sure the part that is erractically clicking now is shorted out. im needing the name of this part if anybody can help me. its 2 black boxes one above the other. both with gray plastic handles (reminds me of a main breaker each one) and both has wires coming into it.
Yes,I have a2002cl500mercadies,stuck in 2nd,with a limp mode code how can I get it out of limp mode?
My 99 mercedes is doing the same thing,if ya ever found out how please email me and tell me,3 mechanics have said 3 seperate things…
I have recently taken over managing 300 Fleet vehicles. A number of my drivers have experienced their Vauxhall Astra Diesel Estates going into Limp Mode.
Currently I have 7 vehicles (different years of manufacture) off the road, as drivers are too concerned to go back into the. As they have all had the reoccurring problem more than once in the same vehicle, usually whilst on the motorway at speed.
I am working with Vauxhall to seek assurance on the safety of the vehicles. I have one vehicle which they have just reset the warning system. I wondered, if the vehicle is safe to drive, I am seeking independent view, as I want to be confident my drivers are safe.
Hey, i know this is a long one but I have a Nissan Sylphy 2006, and it does have a problem with power. First off, i do experience a delayed driving force when i step on the gas especially when the engine is hot and not in motion. This happens more so when a high torque is needed for the vehicle to move either foward or backwards. For instance when i come to a complete stop and i have to go over a bump or ramp of some sort, stepping on the gas wont make it go over immediately as i will have to deeply accelerate for a few seconds..say 7 sec..for it to even start moving. Its movement will be extremely slow until it gains momentum and after which everything works as its supposed to. Whilst all these happens, the rev conter on the dash stays stationery and does not act as though there’s any acceleration at all up until the vehicle moves. It wont rev on neutral too and the ”R” for reverse wont show on the dash board as it goes blank when being reversed. My Mech had to change the throttle sensor, had its transmission control unit replaced and also checked the exhaust system for any leakages but no show. I have constantly stayed dirty on it, moving shop to shop but it seems to prove a headache for everybody. Any help/suggestions will be highly appreciated
what happens if my can fails will limp home mode work or my vehicle will go off road?
2002 Jag vaderplas is in limp mode engine light is on….What to do next…Does it mean tranmission replacement ?
2010 Honda CRV replaced third gear pressure switch light is still drive light is still flashing what do I do next
Does anyone have my answer yet
Not necessarily…could just have sensors not working…have to get yr computer scanned..could also be a selector problem, a loose cable ..
Driving my Nissan Titan, 2009, 165k miles, at fast highway speed with single axle, empty 5’x10′ trailer just now, found engine reving but not transmitting much power to rear wheels; stopped, checked trans fluid level, only 1/2 quart low. Also downshifts with a small “clunk”; my 5 speed auto always shifted perfectly smoothly in the past…
Check engine light has been on 8 months, over catalytic converter code (I got thru Advanced Auto free test); but light went out JUST long enough to have it inspected though, – last September. Too poor/cheap to want to fix it until Sept 2018; may have to do it sooner now: My (good) mechanic actually answered the phone on a Sunday, just now: first question was RE:” any catalytic converter problems”?
SoIm Limping home, at 50 mph; , & Going in tomorrow to see if I’m in “limp mode,” or somehow, I fried my (otherwise trouble-free) transmission… hoping its limp-mode! –Much rather spend $500 on cat converters, than 3,500 on transmission!
Clunking noise is definitely a U-Joint. Reaching under vehicle isn’t fully accurate. replaced all U joints and problem was resolved on our Titan. I am not a licensed Mechanic but have been working on my vehicles since my military days. (80’S)