How faulty ABS can stop automatic transmission from shifting


Your car's ABS system is a technology towards a greater safety and uptimum driving comfort.

However, it's malfunction can result to so many problems in the car. ABS malfunction can stop many other components of the vehicles from working properly or not even working at all. 

For example Toyota Corolla 2008, with electronic power steering and speedometer, if its ABS ECU is malfunctioning, it'll stop the power to the steering and the speedometer will stop functioning. The same things happen to All other Toyota vehicles from 2003 model to latest that are equipped with the ABS system.

What we're discussing now is about Toyota vehicles 2003-2012 that are equipped with the ABS system. This discussion also applies to Lexus vehicles of the same year as the Toyota mentioned

Here are what you'll learn 
  1. Technology behind Wheel speed sensor
  2. How the wheel speed sensor can stop the work of the transmission overdrive. You'll also learn how you'll diagnose the faulty components of the ABS, even without Scanner and without trial and error
  3. How you can turn off ABS warning light after solving the problem,  without scanner. When ABS warning light is on, it means the the motor has been shutdown and it doesn't mean that the faulty part(s) you've replace is not functioning. You need to know how to clear the fault codes stored in the vehicle's computer to re-engage the ABS motor.
Wheel speed sensor or ABS wire

ABS wire is one of the four components of the ABS system. It's attached to each wheel of your vehicle, to sense the rotational speed of the wheel, and sends the signal to the ECU. The speed of the wheel is used to detect when and where to engage the overdrive of a vehicle.

In automatic transmission vehicle, gear only select based on the instructions from the ECU of the vehicle, the ECU only command the shift solenoid to shift to the required gear when it receives signal from wheel speed sensor.

Using the principle of electro-magnetic induction, the permanent magnet of the Sensor and the moving  driving shaft of the vehicle form the two pairs that will generate a voltage, which will be sent to the vehicle's computer to either calculate the stopping distance of the vehicle when you apply brake or to instruct the shift solenoid to engage in higher or low gear.

Accurate and optimal works  of the ABS wheel speed sensor will help in
  • Avoiding Engine suffering: when you're driving at 80 km/h, for example, your car rpm should maintain 2,500 to 3,000. This will help in ensuring excellent fuel economy, longer livespan of the Engine and uptimum temperature will be maintained. When the ABS is disabled, at 80 km/h, you'll notice your rpm above 4,000. The noticeable thing in this type of vehicle is that you'll buy fuel more often than usual, secondly, your engine will be making too much noise and will not move to that extent. 
  • Having greater control over the vehicle. When your ABS is working, you'll hardly experience wheel spinning or any shock when you're taking off. You'll always be in control
  • Gear overdrive will engage in time: when ABS wires are working, your gear overdrive will not let your engine suffers before  it engaged. Automatic transmission engaged to an overdrive at a speed above 90 km/h or when RPM is above 4,000. When this is achieved rpm needs to balance the work of the engine by maintaining a stable state, typically between 3,000 to 4,000 at a high speed. 
How ABS  malfunctioning can stop the work of your transmission
An automatic transmission only shift a gear on an instruction from the ECU, when it receives a signal from a wheel speed sensor. When the sensor says  ' hay Mr ECU,  the speed of the wheel now is 20 km/h,' the computer will tell Mr solenoid to shift to the second gear, and so on it continues till it reaches an overdrive solenoid. But on the absence of the wheel speed Sensor, and the main speed sensor is not programed to measure the speed of the wheel, your car will enter limp mode. Limp mode is when you only drive on the first gear at a maximum speed of 20 km/h. No matter how you press the throttle, the speed will not change. It's also called the safe mode. It's simply telling you that the vehicle is not safe to drive above that speed.

As I said earlier, wheel speed sensor, work with the driving shaft or a wheel hub  to create an induction, which will be sent to the ECU. Now when there's is an obstruction,  like build up of dirts on the plate of the wheel or there's a crack to the wire, it'll stop the work of the wire. It's a very sensitive system that a little debris can stop its works. This might cause it to work haphazardly, or stop working completely immediately. 

When it's not sending signal again, the ABS motor will be shutdown, prompting the yellow warning light on the dash. Like the one below.

Other components like speedometer, electronic power steering (P/S), vehicle stability control (VSC), electronic brake distribution (EBD) will all shutdown with their warning lights showing on the dash in some vehicles

This shouldn't be a problem as long as your transmission is working properly for older vehicles. Unfortunately the new model vehicles will also shutdown the transmission shift solenoid if ABS is shutdown.

If  you're not good in car diagnosis you might end up replacing wrong parts, spending huge sum of money, before you realize this. Some people will replace the whole gearbox, but which will never solve the problem.

How to diagnose ABS Fault(s)
without special tool or a Scanner
In engineering, mistakes from trial and error are always costly, if not your your life, it'll cost your time or money.  So our quest is how can we find the exact answer to our problem without causing another harm nor wasting valuable time. It's not funny after wasting about 5 hours, trying to replace a part but later found out that, it didn't solve the problem.

Now what you'll learn, is how you'll diagnose the fault of your ABS, by reading the fault code directly from your own car dashboard. 

Here we go...

The ABS ECU has a self-diagnostic system which monitors the input and output circuits. The ABS ECU operates the solenoid valves and the pump motor in sequence in order to check each respective electrical system. This function operates only once each time the ignition switch is turned ON. On some earlier models it operates when the vehicle is traveling at a speed greater than 4 mph with the stop light (brakelight) switch OFF. During this check the operation of the actuator can be heard, however this is normal and does not indicate a malfunction.

When a problem is detected in any of the signal systems, the ECU turns on the ABS warning light in the combination meter to alert the driver that a malfunction has occurred. The code is stored in memory for access at a later time. Diagnostic trouble codes (DTC) can be read from the Warning light. 

The ABS ECU will also store the diagnostic trouble codes for any ABS malfunction.
To access the diagnostic trouble codes stored in the ECU, locate the DataLink Connector (DLC1) or (DLC2). The point you're plugging your scanner, see the image below.


 Consult the Repair Manual or the ABS Reference Card to determine whether the ABS Check Connector is physically disconnected or the short pin for Wa and Wb is removed.

To access diagnostic codes:
Watch the video below for full understanding of the explanation below.
The video shows how to read and clear ABS codes.

  • Disconnect the check connector or remove the short pin in DLC1.
  • Jumper terminals Tc and E1 (pin 4 and pin 13) of the Data Link Connector (DLC1 or DLC2.
  • Turn the ignition switch ON and read the trouble code from the ABS warning light on the Combination Meter.
  • Consult your vehicle DTC manual for the interpretation of the codes 

If the computer has not detected a malfunction, the lamp will blink two times per second after a two second pause. When a malfunction has been detected there will be a 4 second pause, then the first digit will begin. The number of times the lamp blinks before a one and a half second pause is the first digit of the code. Next, the number of blinks before the second pause is the second digit of the code. If there is more than one code, the code with the lower smallest digits will appear first.

How to clear ABS codes and turned off Warning light.

Following diagnosis and repair, clear the trouble codes stored in the ECU. The procedure will vary depending on the model and year. Either refer to the ABS Reference Card or Repair Manual for specifics. The essential difference is in disconnecting the actuator check connector on earlier models as compared to the removal of the short pin connector in the DLC1 or DLC2 connector. A typical procedure is outlined below:

  • Jumper terminals Tc and E1 (4 & 13) of the DLC2 or DLC1 and remove the short pin from DLC1.
  • Turn ignition switch ON.
  • Depress the brake pedal 8 or more times within 3 seconds.
  • Check that the warning light shows the normal code.
  • Remove the jumper wire and reinstall the short pin.
If you're using Toyota RAV4 2005-2012,  watch the above Video. The method described is used to read both ABS trouble
Codes and check engine light.

To ensure that the brake light switch opens and closes each time, allow the brake pedal to return to the full up position each time when clearing codes. If the code does not clear, the ignition switch must be cycled OFF then ON before depressing the brake pedal 8 times in 3 seconds.

Note: the code will not clear if the problem is not solved and the warning light will remain on. The ABS code will not clear by removing the battery head as is done on Check Engine Light. 

At Dreamlandmotorworks our work is according to your car's repair and service manual, to make sure the faulty part(s) are replaced. We strongly consider your budget on our diagnosis that's why we nail down to the actual parts at fault.

Unless the part is seen to start malfunctioning in the nearest future, we'll not replace it arbitrarily at Dreamlandmotorworks. Your peace of mind is our overall goal and that's what you'll get if we work for you. You can give us a trial by booking an appointment with us here.

 Our works are:

  • Engine diagnosis
  • Engine overhauling
  • Suspension, brake and clutch repair
  • Body works and painting
  • AC Servicing
We're at 12 King George V Road Onikan, Lagos. Book a free appointment here


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