Engine troubles often cause performance concerns. However, they are frequently hardly perceptible. Therefore, you should not operate the vehicle until the problem has been fixed if you cannot go at speeds of more than 20 mph. The cost of fixing the engine will be high, but before we draw any conclusion, let us quickly go through all the possible reasons.
Your car likely enters safe mode (also known as limp mode) due to an underlying problem if it abruptly stops moving over 20 mph. Moreover, ensure the gearbox changes correctly since it can be stuck in first gear, restricting the speed. It might be a blocked DPF filter or a collapsed catalytic converter; however if the car had performance troubles that had developed to this stage.
Limp Mode
Before we describe how to resolve this, it is important to understand what limp mode is. The engine enters limp mode when the ECU (engine control unit) detects a fault with one of the powertrain systems that might result in significant damage. When a car is in limp mode, the power is drastically decreased, the speed is limited to 20 mph, and sometimes it will not shift out of third gear.
All of these actions are taken by the ECU to reduce future potential harm and to make you address the root cause as soon as feasible. Sadly, there is no simple method to determine what could be the problem, making it essential to read the error codes using an OBD2 scanner. Nonetheless, problems with the timing belt or chain or one of the emissions control systems remain one of the most typical reasons.
Also, you may remove the error codes and unlock the ECU’s limp state using the OBD2 scanner. Yet, depending on what is causing it, the engine can restart in limp mode immediately or a few miles later. So, the only option to get out of limp mode is to check the fault codes and address the underlying issue. The ECU will then automatically leave limp mode after you have done that.
Collapsed Catalytic Converter
The exhaust system that controls emissions includes the catalytic converter. It then transforms certain hazardous exhaust gas molecules into more ecologically friendly ones when the exhaust gases pass through them. For instance, it changes hydrocarbons into water and carbon monoxide (CO) into carbon dioxide (CO2).
Imagine hundreds of small exhaust pipes arranged in a honeycomb pattern within the catalytic converter. Moreover, the honeycomb structure collapses and obstructs the exhaust when the catalytic converter fails. The exhaust block will greatly impact the engine’s performance, resulting in slow acceleration and a constrained peak speed.
Moreover, the catalytic converter may abruptly fail, giving you the impression that something more severe is wrong. But if you also experience additional signs, such as a sulfuric odor, exhaust smoke, and excessive engine heat, you may be certain the problem is with the catalytic converter.
According to repairsmith.com and AutoZone, replacing a catalytic converter may cost anywhere between $500 and $2,200. Yet, the price will range from $500 to $700 for a typical automobile that is roughly 10 years old.
First gear stuck in the transmission
Only cars with automatic transmissions are covered under this section. Also, you can usually tell whether the transmission is moving if it is stuck in first gear, which is the situation if you can only travel at 20 mph.
But, for our less experienced drivers, pay attention to the RPM gauge and where it is at the 20 mph mark. It is in first gear if the engine is roaring, the RPMs are high (near or at the red portion of the rev meter), and you can not feel the gearbox changing.
Be aware that driving your automobile in this manner might do a lot of irreparable harm before we discuss the reasons. And if you must drive it, try to keep your speed to no more than 10 mph.
The torque converter or shift solenoid in your vehicle may be at fault if it will not move out of first gear. However, the car will need to be inspected since it will be hard to determine the precise problem without it.
Yet, for the time being, we may estimate that a defective shift solenoid will cost around $500 to replace, but a new torque converter would likely cost well over four figures. But this specific post has additional information concerning the gearbox being stuck in first gear.
Clogged DPF Filter
The architecture of a DPF filter is quite similar to that of a catalytic converter. In other words, a portion of the exhaust has an inside honeycomb structure resembling small exhaust pipes. The difference is that a DPF filter collects microscopic particles or solid debris, while catalytic converters reduce gaseous pollutants.
Despite having a regeneration mechanism designed to burn those particles away, the DPF naturally jams up over time because it collects microscopic particles. Of course, the engine performance will suffer greatly if the DPF becomes clogged. It is simpler to identify since the performance decline is not as abrupt as other factors on this list.
One solution would be to replace the DPF with a new one, but few people choose to do so due to the high cost—anywhere between $2,000 and $5,000—. DPF filters are instead thoroughly cleaned, and then they are restored to like-new condition.
According to mydpfcleaning.com, the cleaning costs between $350 and $600, which is not exactly inexpensive either. Yet again, you will find a solution as if you had replaced the issue.
Why Does the vehicle not Accelerate Once I Press the Gas?
When you push the gas pedal, the MAF sensor is possibly filthy or broken if your automobile does not go forward. If cleaning it does not work, scan the vehicle for problem codes and work your way back from there. Other typical reasons include a bad throttle position sensor, a bad fuel filter, a bad O2 sensor, or a bad electronic throttle body.
What Does It Mean When My Vehicle Would not Pass 40 Mean?
The probable reasons for a vehicle that will not drive faster than 40 mph, 30 mph, or 20 mph are essentially the same. They include a collapsed catalytic converter, a clogged DPF filter, an ECU that has entered limp mode, or a defective gearbox. Yet, the limp state is the most probable of all the possible reasons.
Would a low oil level prevent the car from accelerating?
No, the automobile will not stop moving forward because of low oil. But, if the oil is dangerously low (you can not see it on the dipstick), the oil pressure will decrease. And when that occurs, the vehicle may go into limp mode or, if the lubrication is inadequate, the vehicle may lose power due to increased friction between moving components and then overheat.
Why Does My Car Have a Speed Limiter?
A safety electronic speed limiter is probably engaged if your automobile is restricting your speed. The onboard computer may be used to toggle on and off the speed limitation, a safety feature designed to stop minors from speeding. To access certain functions, you may require the admin key, however.
Why Would not My Vehicle Raise Its RPM Over 2000?
If your car will not rev higher than 2000 rpm and stops at precisely the same rev every time you floor it, the vehicle may be in limp mode, or the electronic throttle body may malfunction.
The electronic throttle body fuse and relay should be checked first, and then the fault codes should be run if everything seems OK. But, if the engine speed changes when you crank it at roughly 2000 RPMs, it may be a technical problem, such as a blocked fuel filter or a broken MAF sensor.
What Causes My Vehicle to Feel Slow?
If your automobile has a defective throttle position sensor, a filthy MAF sensor, a bad O2 sensor, a blocked catalytic converter, or issues with the fuel or ignition system, it may seem slow. But since there are so many different reasons, you should check the fault codes first to see whether the ECU has any information that may be useful.
What Sensor Is Limp Mode Caused By?
The crankshaft and camshaft position sensors are most often responsible for limp mode. This is because both sensors alert the ECU to an incorrect engine timing situation, which may result in severe damage. For the same reason, the coolant temperature sensor and the oil pressure sensor could also be included in the limp mode.
Can I clean my own DPF filter?
You can clean your DPF filter yourself, but it will not work as well as professional cleaning. The first technique involves utilizing gasoline additives to clean a DPF filter. While avoiding or at least delaying blockage is advisable, even if that approach is the simplest, it will not assist with a severely blocked DPF. The second approach is to remove the DPF and purchase specialized cleaning agents, but keep in mind that this approach will take a whole day and is not as efficient as hiring a pressure cleaner.
Conclusion
In the end, the possibility that the ECU-activated limp mode is the biggest if your automobile will not move faster than 20 mph. This is particularly true if it occurs unexpectedly and the automobile rapidly accelerates to 20 mph.
The check engine light is an even more evident sign that the limp mode is on. If it occurs abruptly, you may be dealing with a defective shift solenoid and other transmission-related issues, and the vehicle will not change gears even in manual mode.
Last but not least, you should check your catalytic converter since it may have collapsed and blocked the exhaust or check & clean the DPF filter if your vehicle has one if it sometimes would not drive above 20 mph or had notable performance difficulties before.