4

Is my reasoning here a plausible explanation for the issues described below?

Background

The CEL on my friend's 2003 Mazda6 lit up yesterday, along with a flashing HOLD light. We hooked it up to a code scanner and found the following codes stored:

P0767 - Shift solenoid 'D' Stuck On
P0841 - Transmission Fluid Pressure Sensor/Switch "A" Circuit Range/Performance
P0733 - Gear 3 Ratio Incorrect

The car was not shifting beyond a certain gear while the CEL was on. We used the scanner to clear the codes and CEL light and then went on a brief test drive in which the issue did not recur and the gear shifts were routine.

We also found the transmission fluid was very clean, but the level was very high. I've requested the car to be taken to a mechanic where some of the excess can be drained out.

The friend says this is the first time this issue occurred. The unusual thing he did was drive the car immediately after starting it up; he normally leaves it to warm up slightly before driving.


Here's what I think happened

My suspicion is the P0841 is the reason behind the CEL, which was triggered by a combination of a request for Gear 3, the ATF level being too high and the fluid relatively cold.

If there is too much ATF in the transmission, I suspect that the pressure sensor may "malfunction" because it is reading an unexpectedly high pressure.

I also believe that the P0767 is just indicating that the transmission couldn't shift gears when needed, while P0733 is just indicating which gear it had trouble shifting into (Gear 3).


On the contrary

It could be that there really is a stuck solenoid inside the transmission, but the condition of the fluid on the dipstick leads me to think otherwise.

Of course, it could be that a previous owner attempted to fix this issue by refreshing the ATF (as opposed to routine preventative maintenance), but that is something that can only be verified by cracking the transmission open.

  • The biggest issue I've seen with excess fluid is blowing out the seals. This is because of excess pressure, so this is completely plausible to me. On the flip side, without impugning your mechanical ability, are you sure you checked the fluid correctly? Some vehicles require you be in Neutral and some in Park when you check the fluid. Could also be the previous owner didn't check the fluid hot and overfilled it. Just throwing it out there. – Pᴀᴜʟsᴛᴇʀ2 Aug 11 '15 at 12:47
  • @Paulster2 : I'll have to check the owner's manual to see what they say about checking ATF level. Seems plausible that someone filled it while the fluid was cold, though I'd expect the fluid level to be at the hot mark when cold if that was the case. In the other question I mentioned that even with the fluid cold the level was above the hot mark. – Zaid Aug 11 '15 at 12:53
  • Yes, I read this question first and commented. That's a lot of extra fluid any way you look at it. – Pᴀᴜʟsᴛᴇʀ2 Aug 11 '15 at 13:04
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Update

It turns out that the transmission was indeed overfilled. The owner said that a lot of transmission fluid had to be drained to restore parity.

Although it is still early to confirm that the issue is no longer present, there are some immediate benefits. The gear shifts feel a lot quicker than before and the brakes feel better than before.

I will update this post in case of further developments or if the issue returns.


Further Developments

The same three codes returned today after the car was driven without letting it warm up.

The fluid level is appropriate according to the dipstick both when hot and cold.

The owner also noted that when the accelerator is pressed with the gear in 'D' for the first time after startup the transmission engages after some delay with a jolt, similar to how a manual car jolts forward after revving slightly and dumping the clutch.

  • My thinking is that the P0767 is the culprit and the other two are feeding off of it. It sounds like a sticky or malfunctioning shift solenoid. – Pᴀᴜʟsᴛᴇʀ2 Aug 21 '15 at 20:49

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