You probably already know that an illuminated Check Engine Light (CEL) means that there's an out-of-spec system that's sent a reading to the powertrain control module (PCM), registering a trouble code. You probably also know that it's just a matter of hooking up a code reader device to the vehicle's diagnostic connector (usually under the dash) for quick access to those codes. You can also visit your local Advance Auto Parts for a free scan to retrieve any codes.
The introduction of OBD-II — a standardized set of on-board diagnostic codes across all makes and models — removed a lot of the guesswork around troubleshooting engine and transmission problems. But it's not quite as simple as just reading the codes and replacing parts. There's a certain amount of interpretation and reading of tea leaves that has to happen to fully diagnose the issue. This is because a related problem might cause a trouble code but the particular circuit or system noted in the code might not be the issue.
In addition, there are often several trouble codes stored at the same time so you'll need to be able to deduce what they mean.
P0750 — Shift Solenoid A Malfunction: What It Means
An electronically controlled automatic transmission needs to be able to transmit torque from the engine then match it to the load and the driver's desired rate of acceleration. It achieves this by selecting a gear ratio and shifting gears, just like with a manual transmission. Shift solenoid A is one of the devices that controls the flow of automatic transmission fluid (ATF) within the unit and enables the transmission to shift from 1st to 2nd gear.
A transmission control module (TCM) is what dictates shift points, and a P0750 code means that the TCM does not recognize the specific RPM range where the transmission should shift from 1st to 2nd.
In many cases, a P0750 code may be accompanied by other transmission-related P codes.
Symptoms
- Transmission will not shift out of first gear
- Shift from 1st to 2nd is delayed or harsh
- An engine misfire might occur
- Poor fuel economy
- Vehicle goes into limp-in mode with a top speed of around 35 mph
What Happens if I Ignore It?
Ignoring any sort of transmission trouble code is a bad idea. In the case of a P0750 code, you won't just be restricted to a top speed of around 35 mph (since the transmission can't shift out of 1st) but you're likely to do serious, permanent damage to the unit too.
Diagnosis
First, it's worth mentioning that, in many cases, failure of a transmission component such as a solenoid can be traced back to poor maintenance and dirty, burned transmission fluid. Healthy transmission fluid will be magenta in color. Look for fluid that's darker, brownish and has a burnt-toast smell, as this can often cause problems.
A low fluid level can also trigger this code and cause the same sort of symptoms. Unfortunately, in many cases, a transmission flush and refill isn't going to solve the problem and may just make things worse.
Follow these steps to fully diagnose the problem:
- Freeze frame the information that you get in your first scanner readings.
- With the scanner hooked up, take the vehicle for a drive and gently accelerate up to 30-35 mph.
- Watch the scanner and see if the PCM issues a command to solenoid A to make the shift from 1st to 2nd.
- Failure to shift would definitely indicate a problem with solenoid A, triggering the code.
Repair
If your diagnosis indicates that solenoid A has failed, your best bet is to take the vehicle to a transmission shop for repair. Modern automatic transmissions are incredibly complex and work very closely with the PCM, so disassembly and repair should really only be trusted to a qualified transmission tech.
Have you come across this code before? Let us know about your experiences in the comments.
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About the Author(s)
Jerry Renshaw is a veteran journalist, gearhead and guitar player, and cultivated his mechanical skills by 30 years of turning wrenches to keep one piece of junk or another on the road. He's owned everything from a Chevette to (three) minivans to a fire-breathing Dodge muscle truck, and is constantly keeping up to speed on what's going on in the automotive world.
