Automatic Transmission Slipping Under Load After Fluid Service
A 2015 rear-wheel-drive ute with a six-speed conventional automatic is brought in after a fluid and filter service at another shop. The owner reports flare on the 2-3 shift when towing and a harsh 4-5 shift when cold. Fluid level was checked by the previous shop with the engine off. The transmission has 210,000 km and no prior service history. On road test, the flare appears only above 60 percent throttle, and the harsh shift disappears once fluid reaches 60 degrees C. A scan tool shows no current codes but a stored code for incorrect gear ratio on the 2-3 shift. Fluid on the dipstick is dark but not burnt, and there is no obvious leak.
1. Explain how you would determine whether the fault is fluid-level related, a hydraulic control issue, or internal wear, and what tests you would run.
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First, re-check fluid level using the manufacturer's procedure: engine running, transmission at the specified temperature, in the correct range, cycling through gears. The previous check with the engine off is invalid and could mean the unit is overfilled or underfilled. Second, inspect fluid condition and smell, and check for debris in the pan if accessible. Third, use the scan tool to monitor line pressure, shift solenoids, and clutch adaptions during a controlled road test at the conditions that reproduce the flare. A stored incorrect gear ratio code on 2-3 suggests clutch slip or a hydraulic delay, not just level. Fourth, compare commanded versus actual gear and solenoid current. If adaptions are at their limit or the flare persists at correct level and temperature, internal wear in the 2-3 clutch or valve body is likely. A pressure gauge test on the relevant ports would help confirm. I would not condemn the transmission until level, temperature and electronic control are verified.
2. The customer wants to know whether the other shop caused the problem. How would you frame your findings and protect your position?
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Frame it factually: the transmission has 210,000 km with no known prior service, and the fluid level was checked incorrectly, which may have contributed but cannot be proven to have caused internal wear. Avoid asserting blame without evidence. Explain what is known: the flare is load and temperature dependent and a ratio code is stored, which points to internal or hydraulic behaviour. Explain what is not yet known: whether correct fluid, correct level and correct filter were used. Recommend a controlled re-check and road test, and quote for further diagnosis before any overhaul. Document the vehicle condition on arrival, fluid level and condition, codes, and the customer's description of the other shop's work. Advise the customer they may wish to raise the matter with the other business, but keep your report to observed facts and test results.