What a transmission trouble code is telling you

When the check engine light comes on and a code reader shows a transmission code, it is easy to assume the worst. A code does not mean the transmission is finished. It means the computer saw something outside of normal and saved a note about it.

Most modern automatics are run by a computer called the transmission control module, or TCM. On some vehicles it is built into the engine computer. When it detects a problem, it stores a code and may turn on the check engine light. Many transmissions also go into limp mode, often holding one gear, to protect themselves until the problem is fixed.

Codes that start with P0 are generic and mean the same basic thing across brands. Codes that start with P1 are generally manufacturer-specific and need that brand's information to read correctly. Even the generic ones can be worded a little differently from one brand to another.

P0700 stands for transmission control system malfunction, and it is a messenger. It means the transmission computer has stored its own code and asked the engine computer to turn on the check engine light. The real details are in the transmission computer, so the next step is a scan tool that can read it.

P0715 points to the input or turbine speed sensor circuit. The computer is not getting a good signal from the sensor that measures how fast the transmission input is spinning. Causes include a failed sensor, damaged wiring, a bad connector or, less often, an internal problem. Without this signal, shifting can get harsh or erratic.

P0730 means incorrect gear ratio. The computer compares input speed to output speed and knows what the ratio should be in each gear. When the numbers do not match, it sets this code. In plain terms, something is slipping. Low fluid, worn clutches, solenoid or valve body problems and sensor issues can all cause it. Related codes P0731 through P0735 point to first through fifth gear, and P0736 points to Reverse.

P0740 and P0741 are about the torque converter clutch, which locks up at cruising speed to save fuel and reduce heat. P0740 points to a problem in the electrical circuit that controls it. P0741 means the clutch is not locking up the way it should, often described as performance or stuck off. Causes range from a solenoid or wiring issue to worn fluid, a valve body problem or a failing torque converter.

P0750 points to shift solenoid A or its circuit. The computer uses solenoids to control shifts, and which one is called A depends on the transmission. The cause may be a failed solenoid, a wiring fault or a connector problem. Related codes cover the other shift solenoids.

P0711 means the reading from the fluid temperature sensor does not make sense, a range or performance problem. P0218 means the transmission fluid got too hot. Take an overheat code seriously. Low fluid, a clogged cooler, heavy towing and long stop-and-go crawls in summer heat can all push temperatures up.

If the check engine light is flashing, pull over when it is safe. A flashing light usually means a serious engine misfire that can damage the catalytic converter.

With a transmission code, stop driving if the car is slipping badly, will not move, shows an overheat warning, or is stuck in limp mode. Limp mode is meant to get you off the road, not through the rest of your week. If the car cannot be driven safely, have it towed or call your roadside plan.

What about P0700 on its own? It depends on the code stored behind it and how the car drives. If it shifts normally, get it scanned soon. If it is slipping, stuck in one gear or in limp mode, get it checked before driving further.

A code tells you what the computer noticed, not what broke. P0730 on two different cars can have two completely different causes. Replacing parts based only on a code is how people spend money and still have the problem.

Clearing a code only erases the record. If the cause is still there, the code comes back, and in the meantime you lose information that helps the technician track the problem down.

A code does not mean you need a new transmission, either. Many transmission codes come from sensors, solenoids, wiring or low fluid. A proper diagnosis adds a fluid check, live data, a road test and electrical testing, and that is how a technician tells a bad sensor from a damaged wire or real internal wear.

Write down the code and how the car is behaving: when it happens, in which gear, and whether the car is cold or hot. If your car has a transmission dipstick, check the fluid.

Until it is checked, avoid hard acceleration and do not tow a trailer. Do not just clear the code and keep driving.

Then get a scan that reads the transmission computer, plus a road test. A basic code reader may show only P0700, because the details are stored in the transmission computer.

At GO TIME Auto Repair in Plantation, a transmission code starts with a diagnosis, not a parts order. We scan the transmission computer, check the fluid, look at live data, test the wiring and road test the car. You approve the diagnostic fee first, and we tell you up front whether it is applied to the repair if you go ahead.

Then you get a written price before any work starts, with photos of what we found. If the problem is a sensor or a wire, that is what we quote. Sales tax is on parts only, and you pick the warranty length: 90 days, 1 year or 2 years.

You get a text at each step: checked in, estimate sent, approved and ready. After the repair, we road test the car and scan it again to make sure the code stays gone.