Automatic Transmission problems

Transmission is a very complex part of an automobile, to diagnose transmission problem the actual parts should be inspected and it must be done by an expert transmission mechanic. However, we are listing here some of the transmission problems and its diagnosis based on possible reason that cause the transmission problem symptoms.

Even though we provide a diagnosis of the transmission, the cause that we mentioned is only a possibility and does not guarantee that it is the exact reason for the transmission problem not unless we look into the actual parts. In this case you still need a transmission mechanic to inspect the actual parts to confirm if our diagnosis is correct. Please have a look on the list of transmission trouble symptoms to guide you when you diagnose transmission problem so that you may have an idea of the possible reason why your car transmission behave differently.

Check Engine Light check engine light may or may not be sign of transmission trouble. This can come on due to one of the following reasons.

  • Throttle Position Sensor codes generally mean the TPS is bad, or the throttle plate is somehow out of adjustment. The throttle body may be dirty, the throttle cable may be to tight, the throttle adjustment screw may need to be tweaked. If the vehicle is drive by wire ( a vehicle which does not have a throttle cable) the throttle body may just need to be reset through a factory type scan tool. Symptoms include poor or no throttle response, poor gas mileage, low or high idle, improper shifting (with automatic transmissions).
  • Oxygen sensor codes Generally mean the oxygen sensor has failed. The oxygen sensor is in the exhaust, and reads the exhaust in order for the computer to finely tune the amount of fuel the engine needs. Symptoms include, poor gas mileage, poor power, rough idle, fail emission testing. Vehicle should start and run even if the oxygen sensor is unplugged.
  • Vehicle Speed codes generally mean the sensor has gone bad.
  • Mass Air Flow Codes generally mean the MAF has gone bad or there is a major vacuum leak. The MAF is the main way the engine monitors the amount of air going into the engine in order to determine how much fuel the engine needs.
  • Manifold Absolute Pressure codes generally mean the MAP is bad, or there is a major vacuum leak. The MAP sensor is one major way the computer decides how much fuel the engine needs. Some cars have a standalone MAP, some have a MAP sensor built into the MAF.
  • Engine Coolant Temperature codes generally mean the coolant temperature sensor is bad, or the car is out of coolant. The ECT effects the amount of fuel the computer supplies the engine. Engines need more fuel to start and run when they are cold. Keep in mind the engine almost always has two ECT sensors, one for the gauge and one for the computer.
  • Evaporative Emission Control System codes are generally hard to diagnose without shop equipment. Your best bet is to replace the gas cap and hope for the best. If the code comes back, you will need a smoke machine to properly find the leak. Any decent shop will have one.
  • Gross fuel trim failure is common and has multiple causes. Vacuum leak, bad oxygen sensor, fuel leaking from fuel pressure regulator into manifold, failed fuel injector, bad coolant temperature (ECT) sensor, bad manifold pressure (MAP) sensor, bad mass air flow (MAF) sensor.
  • Knock sensor codes generally mean the knock sensor has gone bad. Can be wiring, almost never is. Very common problem on imports.
  • Misfire codes – suck, squish, bang, blow gone wrong. Poor quality or incorrect ignition parts, failed injector, burnt valve, improper camshaft/ crankshaft timing, improper ignition timing, low quality gas (water in fuel), low compression (bad rings).
  • Catalyst (Cat) codes generally mean the cat has gone bad. Can be causes by a bad oxygen sensor, but that is generally not normally the case. Very hard to test a cat without shop equipment. Bad cats will rarely have any symptoms, if they are plugged they will cause poor gas mileage, rough running, lack of power.
  • Crankshaft Position generally means the sensor has gone bad, or a timing belt that has skipped a tooth. Many vehicles, particularly Audi and VW will throw a Crankshaft Position if the are turned over too many times with out starting. For example, if the fuel pump goes out, and you try long enough to start the car, a Crankshaft Position code will appear.
  • Camshaft Position generally means the sensor has gone bad or a timing belt that has skipped a tooth. Could also be a clogged or failed variable valve timing solenoid gone bad. Generally, a vehicle uses the crankshaft position sensor for gross fuel and spark control, and the camshaft position sensor for fine tuning. Therefore, a bad camshaft sensor may cause a rough idle, or poor gas mileage, or poor performance, but may the vehicle will still run. On other cars loss of a camshaft position sensor will cause the vehicle to not start at all.
  • Idle Control System vacuum leak, failed idle air control (IAC) valve, dirty throttle body. Basically the vehicle has lost the ability to control the idle, either due to the idle control system failing, or some fort of gross fuel trim failure.
  • Transmission codes are never a good sign. Short of a bad solenoid, or maybe a bad torque converter, you generally are due for a transmission rebuild if you have any of the following transmission codes present.

    • P0730 Incorrect Gear Ratio
    • P0731 Gear I Incorrect ratio
    • P0732 Gear 2 Incorrect ratio
    • P0733 Gear 3 Incorrect ratio
    • P0734 Gear 4 Incorrect ratio
    • P0735 Gear 5 Incorrect ratio
    • P0736 Reverse incorrect gear ratio
    • P0740 Torque Converter Clutch Circuit Malfunction
    • P0741 Torque Converter Clutch Circuit Performance or Stuck Off
    • P0742 Torque Converter Clutch Circuit Stock On
    • P0743 Torque Converter Clutch Circuit Electrical
    • P0744 Torque Converter Clutch Circuit Intermittent
    • P0510 Closed Throttle Position Switch Malfunction

    A good reputable shop will be able to diagnose these codes for you. All of our certified shops have state of the art scan tool to facilitate diagnosis process.

Transmission fluid Leak.

Transmission fluid leak can happen due to the following reasons
  • Transmission Pan: Transmission fluid is stored in a pan under the car. Designed to be opened only for maintenance, the pan has a seal that is replaced whenever you service the transmission. Worn or cracked seals will leak under pressure. Generally, a large leak in this area will result in hard shifting or difficulty putting the vehicle in drive. A series of bolts secures the transmission pan to the vehicle. The bolts can loosen over time, causing the pan to leak.
  • Transmission fluid over filled: During the transmission service or transmission flush if mechanic overfill the transmission fluid it can came ot of the transmission vent. All it takes to cure this by draining the excess transmission oil out of the transmission and ten recheck the level to ensure proper fluid level.
  • Worn Rear Main Seal: The rear main seal is where the transmission meets the car engine. This area is protected by a gasket which can become cracked, frayed and brittle over time.
  • Damaged Transmission Fluid Line: Transmission fluid travels through the transmission in a long tube called a transmission fluid line. A hard impact by road debris can damage this line, which is located on the bottom of the car, between the wheels.
  • Leaky Torque Converter: The torque converter is a hydraulic pump which pressurizes the transmission fluid system and moves the fluid throughout the entire transmission. A leaky or damaged torque converter can cause a serious transmission leak.

Unusual Noises – Makes clicking, knocking, screeching, buzzing, whistling, clanking, or grating noises. Unusual sounds can come from hood or rear of car and may include a hum or low whine.

"Morning Sickness" – When the vehicle is cold, it won't move, or it shifts late during the first few minutes of operation.

Slipping – Engine races, but vehicle moves slowly or won't accelerate as it should.

Stalling – Vehicle stalls or labors on takeoff.

Doesn't Go – You place the shift lever in Drive and nothing happens. Even racing the engine does nothing.

No Reverse – Vehicle doesn't move when shift lever is placed in Reverse.

Loss of Power – Passing gear won't engage, and there's no surge of power when you press the pedal to the floor.

Erratic or Improper Shifting – Noticeable early or late shifting. Unexpected shifts, or speed at which shifts occur keeps changing.

Shift Handle Stuck/Sticks – Shift handle is hard to move into or out of any position.

Vehicle Moves (or Jerks) in Park or Neutral – May be when you first start the car or before you turn it off

Strange Smell – Burnt or rancid odor is coming from under the hood or underneath vehicle.

Shift Indicator Off – The indicator must be slightly off (P) or (N) to start the car. Shift indicator doesn't point to the proper range.

Metal Shavings or Debris – Inspection or transmission service reveals excessive amounts of debris in the transmission pan.

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