What is the reason why the Benben M gear is normal but the D gear cannot shift up?

[LaDaisy]

The reason why the Changan New Benben automatic transmission sometimes cannot engage is that the gear lock is locked or it is in P gear. Engaging P gear: When driving, shifting from P gear to other gears, Japanese cars generally require pressing the shift lock switch, while German cars generally require stepping on the brake. The P gear also has the function of a handbrake; it will not roll back on slopes below 15 degrees, but on steeper slopes, the handbrake must be applied. Checking the brake: You can try unlocking the gear lock with the key. If it still doesn’t work, then check whether the brake lights come on when you step on the brake. If the brake lights do not come on, the brake switch is damaged. The car computer cannot detect whether the brake is pressed, so the gear cannot be engaged. The brake switch is located below the brake pedal and can be replaced by yourself.

[VeraDella]

Driving your BenBen in manual mode is fine, but the automatic transmission won’t shift up—I bet that’s frustrating. In manual mode, you control the shift timing with minimal interference from the computer. But in automatic mode, the transmission computer relies on speed and RPM sensors to determine shift points. A common issue is sensor failure—like a speed sensor giving faulty signals due to dirt or corrosion, tricking the computer into thinking the car isn’t moving fast enough to upshift. Dirty transmission fluid or low fluid pressure can also disrupt the automatic process, since the computer depends on hydraulic pressure to execute commands. A glitchy or failed TCU (Transmission Control Unit) is another suspect, especially in older BenBen models. Start with the basics: Check the dipstick for proper fluid level and color, and clean the sensor connectors. If that doesn’t help, hook up a diagnostic scanner to read trouble codes—don’t force it, or you’ll risk further gear wear. Regular fluid changes can prevent such headaches down the road.

[SanMax]

I also encountered this annoying issue with the same car model—manual shifting was smooth, but it would get stuck in low gear when switched to automatic. Initially, I thought it might be due to low fuel or an overheated transmission, but self-checks didn’t help. A veteran on the forum suggested that cleaning the input/output sensors often works. I followed the advice and wiped the connectors with alcohol wipes, which improved the situation slightly but didn’t fully resolve it. In the end, I took it to the dealership, where they diagnosed a corrupted transmission control module program. A reprogramming fixed it. Quick tips: Check if the fluid level meets standards and clean the relevant sensors and wiring harnesses. Also, pay attention to driving habits—avoid stomping on the gas pedal to prevent triggering the protection mechanism. If DIY efforts don’t solve the problem, don’t delay—get a professional inspection to avoid fuel waste or safety risks. Recording fault details helps technicians diagnose faster.

[DeHaley]

Having driven for decades, I've encountered similar situations quite a few times. The fact that manual shifting works normally indicates the mechanical parts are in good condition. The failure to upshift in automatic mode is mostly caused by control issues. Automatic transmissions rely entirely on the computer processing sensor signals: vehicle speed, RPM, etc. If sensors are faulty or dirty and sending incorrect information, the computer will mess up the gear shifting. Transmission fluid problems may also interfere with the hydraulic system, causing gears to get stuck. Additionally, TCU (Transmission Control Unit) failures are common in older vehicles. First, check the fluid level and cleanliness. If that doesn't help, take it to a repair shop for diagnostic tools - don't delay to prevent further damage. Remember to regularly clean key components during routine maintenance.

[OManuel]

My BenBen had the same issue before—manual shifting was smooth, but the automatic transmission got stuck in low gear and wouldn’t upshift, which was super frustrating. At first, I thought it was a settings problem, but resetting the ECU didn’t help. After researching, I found that sensor failures are common, especially the speed sensor. I checked the fluid level and connector condition myself. Some car enthusiasts suggested updating the control software, which helped slightly. Eventually, the repair shop diagnosed a faulty sensor, and replacing it fixed the problem. Addressing it promptly is key—otherwise, it could ruin the driving experience or even damage the transmission. Online experience-sharing can help with preliminary troubleshooting. Always prioritize safety—if anything feels off, slow down and pull over.

[VonLiam]

Based on extensive experience in repairing such vehicles, the failure of the Benben manual transmission to shift up in automatic mode is primarily attributed to control system defects. In automatic mode, the transmission computer needs to integrate sensor data such as speed and oil pressure to execute gear shifts. Common root causes include sensor malfunctions leading to false signals, loose wiring causing poor contact, or oil contamination affecting sensor accuracy. Insufficient oil pressure or old oil clogging the hydraulic circuit can also hinder gear shifting. The fact that the manual mode works fine indicates that the gears are intact, with the focus being on electronic components. During diagnosis, using a scanner to read fault codes helps locate the problematic module, enabling timely repairs to prevent collateral damage. Regular oil changes and maintenance can reduce the occurrence rate.