Building the A5HF1 and A5MF1 units have become almost second nature to builders in larger, metropolitan areas. These units are more predictable than their parent unit, the KM. But they can become annoying and overbearing if you don’t pay attention to details that could mean the difference between a job that stays gone versus one that has many unhappy returns.
Let’s look at the A5HF1 in a 2006 Hyundai Sonata with a 3.3L engine (VIN F). Shift quality issues are an all-too-familiar customer complaint for these vehicles. The most common shift issue is a 2-3 flare with no codes. Check engine light on and intermittent electrical issues are popular, too.
If the vehicle can be test driven, take every advantage to look at sensor data. Take a movie of transmission and engine data before, during, and after a fault occurs. For intermittent issues, wiggle test the transmission main harness and speed sensor pigtails while operating the vehicle on a lift. Once these vehicles exceed factory warranty, they tend to exhibit electrical problems.
After assessing the overall electrical health of the vehicle (including static battery charge and alternator output), perform a global scan and software level scan and record all codes and programming part numbers.
Check for bulletins regarding the customer’s complaint to see if the vehicle needs programming. Most of these units do have TCM shift quality programming updates that should have already been performed.
Now you’ve ready to perform a targeted repair or pull the transmission for an inspection and rebuild. In either scenario, here’s where detail is very important. Air checks on disassembly and basic parts inspection will reveal obvious issues, but it’s easy to overlook bushing or valve body wear. You can direct your focus on certain areas based on failed and stressed components inside the transmission.
Understanding the pressure management strategy for this unit is important in diagnosing failures. Just like earlier, KM-type units, the A5HF1 applies full line pressure to the clutches and band while they’re applied. The system reduces pressure to control shift feel. The VFS solenoid, along with the pulse width modulated shift solenoids, control the transitions (figure 1).
If all shifts are having issues, you may have trouble with overall line pressure control. A common problem is bore wear at the pressure regulator valve. Inspect the bore carefully, especially if you’re having lock-up related problems.
If specific shift transitions are the complaint, look for trouble with the valve body or individual shift solenoids. Using the clutch-and-band apply chart (figure 2a), along with the solenoid apply chart (figure 2b), you can locate specific control related problems.
With the unit on the bench, give special attention to the valve body. There’s a pressure control valve directly associated with each shift solenoid (figure 3). The valves manage line pressure directed to the clutch in the hydraulic circuit they control. When they stick or don’t move freely, it can affect clutch apply-and-release rates directly, causing binding or flared shifts.
Also notice that, even though these valves look similar, there are differences. The underdrive and low/ reverse clutch pressure control valves have an extra land, compared with the other clutch pressure control valves. There’s a cross-drilled orifice on these valves (figure 4). It’s part of the clutch release (exhaust) hydraulic circuit. Always make sure the orifice is clear.
Another situation unique to the A5HF1 is a complaint of a 2-3-neutral shift. This can be the result of a cracked reverse piston (figure 5). The overdrive clutch uses the reverse piston internal surface area as a part of the apply circuit.
In this case, neither the reverse nor the overdrive clutches may show signs of trauma. The piston may crack and cause this condition. Inspect and replace it as necessary.
The transmission temperature sensor is another weak link with this transmission as well as other 4-, 5-, and 6-speed variations of this unit. Replace the original sensor with the updated OEM sensor, part number 46386-39050.
For some reason, the 2-3 shift transition is the most problematic for this unit. Check for ring land wear, clutch drum ring surface wear, internal piston housing wear from debris getting caught between piston seals and the drum, unit endplay, and all bushing-to-journal clearances (figure 6). Assume anything here could be the cause of a subsequent 2-3 shift issue.
Once all is well inside the unit, it’s time to install the transmission and test drive the vehicle. Here’s where things can go wrong, and often do:
- Let the vehicle reach operating temperature.
- Check and top off the fluid level.
- Shift through the gears no fewer than five times.
- Engage forward to reverse five times.
- Check and clear any transmission or engine codes.
Important: Make sure you observe the transmission fluid temperature range necessary to initiate the relearn process. It differs between vehicle models and years.
For example, the 2006-2010 Sonata requires that the transmission fluid temperature sensor reads between 50°F and 122°F (10°C-50°C) to initiate the Relearn Adaptive Value process in the TCM. This will be a scan tool-prompted test drive to relearn the clutch adapt values. During this process, you must hold the accelerator pedal steady during upshifts or the system won’t be able to adapt correctly.
For our 2006 Sonata, hold the throttle between 25% and 35%. Make sure you choose an adequate test drive area and obey all traffic laws.
Be aware that most aftermarket scan tools aren’t capable of performing the adaptive values relearn procedure. With some, it’ll appear that this function has occurred successfully, but you won’t notice any change in shift quality.
Hyundai computers have nonvolatile memory. This means that the adaptive values will remain, even if you disconnect the negative terminal of the battery. In this case, you’ll need the factory Hyundai GDS tool to perform this function.
I recommend a trip to the dealership as a part of the repair package. Refer to the chart for vehicles that require the OEM GDS tool or equivalent (figure 7).
Caution: Never disconnect the battery cables (positive or negative) and cross them together in an attempt to “brain dead” the computer. On Hyundai applications, this could damage the computer or corrupt its programming.
If shift quality improves, you can perform additional adaptation by manually downshifting at moderate throttle (5-4, 4-3, 3-2, and 2-1). Perform this three to five times. Then perform several forced downshifts (5-3, 5-2, and 3-1) at 1/2 to 3/4 throttle.
If engagements are an issue, you can adapt the garage shift into drive by shifting P-N-D-N-P, stopping three to five seconds in each position. Repeat this five times.
You can do the same for reverse: Perform P-N-R-N-P, stopping three to five seconds in each position, and repeat the sequence five times.
All things considered, these units can be routine success stories by taking a little time to look at the details more closely. Often, planning a little side trip will help!