Just Lost 3rd Gear in Auto Transmission Can I Continue to Drive on the Hwy at 55 Miles Per Hour

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.

Need a replacement transmission? Get an estimate for replacement transmissions and local installation. Look up your transmission model by vehicle make and model.


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

Check Engine Light - Limp Mode

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.

Fault Code Diagnostic Scanner

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:

Need a replacement transmission? Get an estimate for replacement transmissions and local installation. Look up your transmission model by vehicle make and model.


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

GM Ford Chrysler Other Makes Manual / Standard
4L60E 4R75E / 4R75W 42RLE Nissan RE5R05A T56
4L65E 4F27E A604 / 41TE Nissan RE7R01A T45
4L80E 4R100 46RE Nissan RE4R01A T10
4T45E 4R44E 47RE Nissan CVT AX15
4T40 5R55E / 5R55N 48RE Mercedes 722.6 AX5
4T65E 5R55S / 5R55W 45RFE Mercedes 722.9 Jeep NSG370
4T65E-HD 5R110W 545RFE Toyota AB60E TR-3650
4T80E 6F35 62TE Toyota U241E NV5600
5L40E 6F50 65RFE Toyota A750E NV4500
6L80 6R60 68RFE Toyota A750F NV3550
6L90 6R80 W5A580 / NAG1 Toyota A340F NV3500
6T40 6R140 F4A42-1 Toyota A340E G56
6T45 10R80 F4A42-2 Toyota A650E MT82
6L45 / 6L50 AX4N / AX4S F4A4B-1 Toyota A541E 5MT
6T70 AWF21 F4A4B-4 Toyota A246E
6T75E CD4E 948HP Toyota A245E
8L90 FNR5 Aisin AS68RC Toyota A140E
8L45 TF-80SC Aisin AS69RC Toyota V4A51
9T65 GF4A-EL ZF 5HP24
9T50 JF506E ZF 6HP19
10L80 A4LD ZF 6HP26
Allison 1000 C6 ZF 8HP70
TH400 AODE ZF 8HP75
TH350 E4OD ZF 948HP
700R4 AOD Honda BYBA
Aisin AW55-50SN Honda MZHA
Aisin AW55-51 Honda MKYA
Honda MZJA
Honda MT4A
Honda SPCA
Honda B0YA
Honda BZHA
Honda B4RA
Honda B6VA
Honda B7TA
Honda B7TA
Honda B7WA
Honda BVLA
Honda B7XA
Honda PN3A
Honda BAXA
Honda P36A
Honda BCLA
Honda GPPA
Honda PGRA
Honda BDGA
Honda B97A
Honda BGHA
Honda BMXA
Honda BVGA
Honda SMMA
Honda SP5A
Honda MCVA
Honda M6HA
Honda MDLA
Honda MJFA
Honda BJFA
Honda MJBA
Honda MRMA
Honda B90A
Honda MGFA
Honda B5SA
Honda MDKA
Honda MRVA
Honda MDRA
Honda BDKA
Honda BYFA
Honda BB7A

Problems by Make & Model

Model
Acura CL
Acura MDX
Acura TL
BMW X5
Buick Enclave
Buick Lacrosse
Buick Lucerne
Buick Rendezvous
Buick Rainier
Buick Regal
Buick Terraza
Cadillac CTS
Cadillac DTS
Cadillac Escalade
Cadillac SRX
Cadillac STS
Cadillac XTS
Chevy Avalanche
Chevy Blazer
Chevy C1500
Chevy C2500 HD
Chevy C3500 HD
Chevy Camaro
Chevy Cavalier
Chevy Cobalt
Chevy Colorado
Chevy Equinox
Chevy Express 1500
Chevy Express 2500
Chevy Express 3500
Chevy Express 4500
Chevy HHR
Chevy Impala
Chevy K1500
Chevy K2500 Suburban
Chevy Malibu
Chevy Monte Carlo
Chevy S10
Chevy Silverado 1500
Chevy Silverado 2500 HD
Chevy Silverado 3500 HD
Chevy SSR
Chevy Suburban
Chevy Tahoe
Chevy Trailblazer
Chevy Traverse
Chevy Uplander
Chevy Venture
Chevy W3500
Chevy W4500
Chrysler 200
Chrysler 300 - 300M
Chrysler Aspen
Chrysler Pacifica
Chrysler PT Cruiser
Chrysler Sebring
Chrysler Town & Country
Dodge Avenger
Dodge B1500
Dodge B2500
Dodge B3500
Dodge Challenger
Dodge Charger
Dodge Dakota
Dodge Durango
Dodge Journey
Dodge Magnum
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Dodge Nitro
Dodge Ram 1500
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Dodge Sprinter 2500
Dodge Sprinter 3500
Ford Crown Victoria
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Ford F150
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GMC W4500
GMC Yukon
Honda Accord
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Hummer H2
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Hyundai Santa Fe
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Infiniti G35
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Infiniti QX56
Isuzu Ascender
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Isuzu NPR
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Isuzu Trooper
Jeep Commander
Jeep Grand Cherokee
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Lexus GS300
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Mazda 2
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Mazda 626
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Toyota 4Runner
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Volkswagen Jetta
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Volvo C70
Volvo S40
Volvo S60
Volvo S70
Volvo S80
Volvo V40
Volvo V50
Volvo V70
Volvo XC70
Volvo XC90

OBD2 Transmission Trouble Codes

DTC Code
P0218
P0702
P0705
P0730
P0740

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Source: https://www.transmissionrepaircostguide.com/limp-mode/

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