Why Is My Check Engine Light On and My Car Won’t Shift Properly?

Seeing the check engine light and experiencing shifting problems at the same time can be alarming. If your car won’t shift properly—whether it’s hesitating, slipping, or stuck in a single gear—this combination often points to a transmission-related issue. While many assume the light is engine-specific, today’s vehicles connect the engine and transmission control systems closely, meaning one can easily affect the other.

This article covers what causes the check engine light to come on with poor shifting, how to start diagnosing it, and when to call in a transmission expert.

How the Check Engine Light and Transmission Are Connected

Modern vehicles have intricate systems where the transmission control module (TCM) and engine control module (ECM) constantly share information. When something interrupts the communication—like a failed shift solenoid, a faulty sensor, or abnormal hydraulic pressure—the car stores a fault code and activates the check engine light.

Sometimes, this triggers limp mode, where the transmission limits shifting to prevent further damage. If you’ve also noticed your car revs but doesn’t move, you may be experiencing a similar issue (see our article on why your car revs but doesn’t move).

Common Causes of Check Engine Light and Shifting Problems

Here are some of the most frequent culprits behind the check engine light shifting combo:

1. Failed Shift Solenoids or Speed Sensors
These electronic components control gear engagement and shift timing. If they fail, the car may not shift at all—or may skip gears, delay, or jerk. The system will likely store a code like P0700, which often indicates a general transmission fault.

2. Low or Burnt Transmission Fluid
Fluid issues are a leading cause of shifting problems. Dirty or low fluid prevents hydraulic pressure from building up, which causes delayed shifts and hard engagement. If you’ve noticed a burning smell when driving, this might be a related sign (read more in our post on burning smells while driving).

3. Torque Converter or Internal Wear
When clutch packs or bands wear down, or the torque converter fails to transfer power, you may experience slippage, hesitation, or a total lack of gear engagement. These mechanical issues can also trigger fault codes and the check engine light.

4. TCM or ECM Malfunction
If either control module fails or receives inaccurate data from sensors, the system may prevent shifting altogether. Software updates, reprogramming, or module replacement may be needed.

5. Overheating or Limp Mode Activation
When internal temperatures rise too high, or a major fault is detected, your transmission may lock itself into second or third gear to limit damage. This is usually accompanied by a check engine light, a warning light, and poor drivability.

What You Can Check Before Visiting a Shop

If your check engine light is on and the car won’t shift properly, here are some steps to help determine the issue:

• Scan for codes: A basic OBD-II reader can identify whether you’re dealing with a general transmission issue or a specific component fault.
• Check fluid level and quality: Use the dipstick (if available) to assess whether fluid is dark, low, or smells burnt.
• Note when symptoms occur: Do you feel delays when going from Park to Drive or when shifting at speed? Does the issue improve once the car warms up?
• Look for leaks or overheating: Pooling fluid under the vehicle or extremely hot transmission housing could point to internal wear or seal failure.

If you’re not sure what you’re seeing or feeling, this technical breakdown from NAPA is a good resource to understand what specific signs might mean.

When to Call a Transmission Specialist

A check engine light with shifting issues is not something to ignore. Driving with these symptoms could lead to:

• Permanent damage to the transmission
• Failure to shift into needed gears (especially uphill or at high speeds)
• Unsafe vehicle behavior and breakdowns

At Top Notch Transmissions, we provide expert diagnostics for ECM and TCM errors, shift solenoid malfunctions, and fluid condition assessments. Whether the solution is a software reset, part replacement, or a full transmission repair, we’ll give you straight answers and professional service.

If a rebuild or certified transmission replacement is necessary, we offer industry-leading warranties and local Fort Worth support to make the process as easy as possible.

Get the help your vehicle needs before things get worse. When your check engine light is on and your car won’t shift properly, it’s a sign the system is struggling—and continuing to drive only increases the risk. Our experienced team at Top Notch Transmissions can pinpoint the issue and fix it fast. Book your diagnostic today and drive with peace of mind.