A 2001 Volvo V70 XC recently displayed a “Transmission Service Urgent” message accompanied by surging RPMs during acceleration. Prior to this, the check engine light (CEL) illuminated, revealing codes P0030 (HO2S Heater Control Bank 1 Sensor 1) and a generic P0168. While initially dismissed as a minor issue, the vehicle subsequently lost all drive and reverse functionality. A new code, P0735 (Gear 5 Incorrect Ratio), appeared alongside the existing codes.
This scenario points to a severe transmission problem, likely unrelated to the previous O2 sensor code. The P0735 code specifically indicates a problem with the gear ratio in fifth gear. This could stem from various internal transmission failures, such as damaged clutches, worn bands, or faulty solenoids. Fluid issues, although the fluid level was reportedly full and clean, can also contribute to this problem. Low fluid pressure or severely degraded fluid (despite appearing clean) could hinder proper gear engagement.
The recent replacement of the right front axle and hub bearing assembly raises the question of potential correlation. While unlikely, improper installation of the axle, particularly a non-OEM part, could theoretically impact the transmission if it interfered with the operation of the vehicle speed sensor (VSS). The VSS provides crucial data to the transmission control module (TCM), and inaccurate readings could disrupt shifting patterns and lead to gear ratio errors. However, this is less probable given the complete loss of drive and reverse.
Given the vehicle’s mileage (148,000 miles) and lack of confirmed transmission fluid changes, long-term fluid degradation is a strong suspect. Automatic transmission fluid (ATF) breaks down over time, losing its lubricating and hydraulic properties. This can lead to increased wear and tear on internal components, eventually resulting in catastrophic failure.
Furthermore, internal mechanical failure within the transmission itself is the most likely culprit. The P0735 code directly points to an inability to achieve the correct gear ratio in 5th gear. This often signifies significant damage to internal components.
In conclusion, the P0735 Gear 5 Incorrect Ratio code, coupled with the complete loss of drive and reverse, indicates a major transmission problem in the Volvo V70 XC. While a connection to the recent axle replacement is possible, it’s less likely than internal transmission damage due to wear, fluid degradation, or a combination of both. Further diagnosis by a qualified transmission specialist is necessary to pinpoint the exact cause and determine the appropriate course of action, which might involve rebuilding or replacing the transmission. Regular maintenance, including timely transmission fluid changes, is crucial for preventing such issues.
