What are the causes of high-low range shift valve failure?
2 Answers
This type of failure generally occurs in the auxiliary box's high-low range shifting control system. When this failure occurs, the driver should first pull the vehicle over to the side. The specific inspection method is to first check whether the vehicle's air pressure meets requirements, then place the gear shift lever in neutral position while stationary. Structure and working principle of auxiliary box: It consists of a power take-off shaft, low-speed gear, synchronizer, left and right intermediate shafts, high-low speed control cylinder, etc. Each of the left and right intermediate shafts has two gears that mesh with the main gearbox's power take-off shaft gear and auxiliary box's low-speed gear respectively. Precautions: During vehicle operation, sudden occurrences of having only high range without low range, or only low range without high range are common failures. This type of failure generally occurs in the auxiliary box's high-low range shifting control system.
I've been repairing cars for over 30 years and have encountered many issues with high-low shift valve failures. The common causes are: first, severe fluid contamination where debris clogs the valve orifice, causing it to jam; second, electrical problems such as short circuits or voltage instability affecting signal transmission; third, mechanical wear where prolonged use makes the valve spool surface uneven, leading to oil leakage or sticking; fourth, excessively high transmission oil temperature due to frequent rapid acceleration or hill climbing, causing overheating and deformation. I've also found that improper maintenance is key—some vehicles don't get timely oil changes, allowing contaminants to accumulate quickly. This fault can cause delayed shifting or even prevent gears from engaging, potentially damaging the entire transmission system. That's why I always remind owners to check fluids regularly and change them every 40,000 kilometers. If noticeable jerking occurs while driving, stop immediately and get it inspected at a shop to avoid minor issues turning into major repairs.
