* Low Transmission Fluid: This is the first and easiest thing to check. Low fluid level can cause all sorts of transmission problems, including pulsing, slipping, and harsh shifting. Check the fluid level with the engine running and warmed up. If it's low, you need to figure out *why* it's low (leak, internal failure) before simply adding fluid. The fluid color and condition (burnt, smell) are also important indicators.
* Dirty or Low-Quality Transmission Fluid: Old, dirty, or the wrong type of transmission fluid can cause the clutch packs to slip and cause pulsing. A fluid change with the correct type of fluid (consult your owner's manual) is often a good first step.
* Failing Torque Converter: The torque converter is a crucial part of the automatic transmission. A failing torque converter can cause pulsing, especially in overdrive where the engine speed is lower relative to vehicle speed.
* Worn Transmission Clutches or Bands: Internal wear and tear on the transmission's clutch packs or bands can lead to inconsistent engagement and pulsing. This is a more serious problem requiring a transmission rebuild or replacement.
* Solenoid Problems: The solenoids control fluid flow within the transmission. A faulty solenoid can cause erratic shifting and pulsing.
* Valve Body Issues: The valve body regulates the hydraulic pressure within the transmission. Problems within the valve body can lead to various transmission issues, including pulsing.
* Speed Sensor Issues: The vehicle speed sensor or transmission speed sensor provides crucial information to the transmission's computer. A faulty sensor can lead to incorrect shifting and pulsing.
* Transmission Computer/PCM Issues: In some cases, a problem with the transmission control module (TCM) or the powertrain control module (PCM) can cause pulsing.
What to do:
1. Check the transmission fluid: This is the absolute first step. Check the level, color, and condition.
2. Consult your owner's manual: This will tell you the correct type of transmission fluid to use and the recommended service intervals.
3. Get a professional diagnosis: If the problem persists after checking the fluid, taking your Grand Prix to a reputable mechanic or transmission specialist is crucial. They have the tools and expertise to diagnose the problem accurately and recommend the appropriate repair. A simple scan tool can often reveal trouble codes related to the transmission.
Ignoring transmission problems can lead to significant and costly repairs later. Address the issue promptly to avoid further damage.
