Overdrive function on automatic transmission car reduces RPM to a certain speed to help in acceleration and provide more fuel-efficient driving. This function can malfunction and cause the overdrive light to blink or flash due to a damaged speed sensor, low temperature, damaged wires or internal issues on transmission.
Though this issue requires mechanical help, knowing how to fix overdrive light flashing can help you avoid expensive repairs and blinking lights. You can also disable the overdrive function though it doesn’t fix internal issues.
Article Summary
How To Fix Overdrive Light Flashing or Blinking?
If your car’s overdrive light is flashing, it indicates a problem with the transmission. It is quite similar to a check engine light. O/D light can flash due to plenty of reasons including bad sensors, low transmission fluid, or damaged wires. If you ignore this light, it can destroy the whole transmission. It’s crucial to understand how to fix overdrive light flashing.
1. Replace Vehicle Speed Sensor
O/D light mostly flashes on vehicles that are equipped with 4R44E or 5R55E transmission. On the 4R44E transmission, a speed sensor is placed near the tail shaft housing that can wear out and cause constant or intermittently overdrive light blinking or flashing. On the 5R55E transmission, a speed sensor is placed inside the transmission.
If the overdrive light flashes and the speed reads zero or something different than right mph, it can result from a bad speed sensor. VSS (vehicle speed sensor) monitors the overdrive system and helps the computer determine the right shift points.
If the sensor gets damaged due to old or contaminated transmission fluid, debris, or corrosion, it can malfunction and provide an incorrect RPM rating. Bad sensors can also cause delayed shifting, hard shifting, or premature transmission failure.
To fix this problem you’ll need to replace the faulty speed sensor that usually lasts around 30,000 to 50,000 miles. In this case, you’ll need to disconnect VSS from the transmission system, remove the connector between the sensor and wiring harness, and remove and replace the sensor. Most mechanics will cost between $200 and $400 to replace bad VSS.
2. Fill Transmission Fluid
Solenoids control the transmission overdrive and fluid pressure activates the solenoid. If there is low fluid pressure, the solenoid won’t be able to activate overdrive gear. Hence overdrive light can start flashing as a warning. To check and fill transmission fluid, remove the dipstick from a tube and clean it. Put the dipstick back and pull it again.
Check the dipstick to read the fluid level if it’s low, full, or full. If you read it as fill or low, you have to fill transmission fluid into the tank. To do so, insert a funnel into the dipstick hole and fill up to the recommended level based on the vehicle’s owner’s manual. Then replace dipstick and test drive.
3. Overhaul Transmission
If your car’s overdrive light flashes randomly and you hear a whining noise, check the fluid pump or internal case. You can hear a high-pitched whining noise from the transmission area if the shift cable vibrates against the turbine speed sensor on the transmission case. If so, you have to inspect the routing of the shift cable and adjust it particularly if it’s rubbing against anything.
Internal case wear is also a common problem for transmission that can cause fluid pressure loss internally, O/D light flash, and gear slipping problems. If this is the case, your transmission will need overhaul or replacement.
4. Repair Faulty Wires
OD switch’s wire travels through the shift lever, crosses over the top of a column, and plugs into wiring harness. These wires allow shifter to move and steering wheel lock which can wear through insulation and expose the wires. In this case, overdrive light can flash and the fuse can blow out.
Overdrive circuit’s wires can also shorten or burn and trigger these issues. However, it is easy and affordable to fix worn-out, short, or burnt wires using a Phillips screwdriver and some tape. To do so, remove three screws that hold plastic trim around the shifter, unscrew tilt steering lever, and disconnect the lower plastic part.
With the ignition switch in on position, press key cylinder’s shiny ball and remove cylinder. Then slip upper plastic piece over shift lever to get access and fix damaged or worn wires. You can also unplug the wire from the harness, remove the pin and slip shifter lever to take whole thing out and repair it comfortably.
5. Rebuilding Transmission
If you have recently serviced maintenance of your car and noticed an O/D light flashing, it needs mechanical inspection. OD light may start flashing after rebuilding and internal issues may trigger it. So bring your car to the auto repair shop and troubleshoot it deeply to determine the exact source and then fix the issue.
Is It Safe To Drive When Overdrive Light Flashing?
If the overdrive light is flashing or blinking, it means something wrong with transmission system components like speed sensors or solenoids. In this case, you shouldn’t continue driving your car. Otherwise, the car will go into protective mode, line pressure will go up and you’ll feel is hard to shift. Your car will also activate limp mode as the computer detects severe transmission malfunction.
So your car will no longer be safe or convenient to drive. If the O/D light is flashing, run a code reader to discover the stored trouble code on your computer. This will help you understand what causing is a problem.
But if the overdrive light turns on and stays consistently on, you can confidently continue driving your vehicle. This light indicates that your car is maintaining a steady speed while driving. This way overdriving mechanism improves fuel economy and reduces wear and tear during driving at highway speeds.
How To Disable Overdrive Light Flashing?
Though the overdrive system is a helpful feature, you can turn it off when driving on rough terrain, downhill, hill, or when don’t need to accelerate. However, disabling the process of overdriving function varies from car’s make and model. Some vehicles have an O/D off button while others have the switch on the gear lever.
On a vehicle with pre pre-designed button, press the button off to disable the overdrive function. To manually disable the O/D function, select lower gear. If your vehicle has an automatic transmission and manual gear shift or paddle shifters, switch to low gears to turn off the overdrive feature.
FAQs
Does Overdrive Off Make The Car Faster?
Overdrive function allows the transmission to move into its highest gear to provide better fuel efficiency. However, it doesn’t make any difference with car speed.
How Much Does it Cost To Fix The OD Light?
Overdrive light flashing problems may trigger plenty of trouble codes including PO750, PO755, PO962, and PO743. Mechanic shops may charge around $3,400 to $4,000 to clear those codes.
How Do I Know if My Overdrive is On or Off?
When the overdrive function is off, an indicator light will appear on the dashboard. It means all transmission gears are in use. When the indicator light is off, the overdrive function is on.
Final Words
Hope you understand how to fix the overdrive light flashing problem. So if the O/D light is blinking or flashing, park your car in a safe spot and check fluid level. If there is no problem with transmission fluid, carefully drive your car to the nearest mechanic shop and diagnose properly. Don’t ignore or disable overdrive light and continue driving if it flashes unless you want to damage the transmission.
