Automatic Transmission troubleshooting

JayCab — Sat, 26 Sep 2026 23:38:50 GMT

Hello Forum!

I have the following problem with an 01N DFM 4 speed auto in my Cab;

1. Primary complaint: Sometimes, especially on initial pull-away, it's slow to change into 2nd gear. When it does this, it always changes at exactly 3.5K RPM, and usually for one shift during a drive cycle, and usually the first shift. The delayed first 1-2 shift is never at any RPM other than 3.5K when it happens.

2. Point 1 is in the presence of no other problems.
More symptoms:
--> Fluid is genuine, clean, with no metallic shrapnel or particles ever seen coming out of the pan or shimmering in the fluid on fluid change
--> Filter is genuine , new, clean.
--> Zero fault codes sustained over 1K+ miles for both ECM/TCM.
--> Car (and original transmission) is at 88K miles (I owned it from 69K @ 23 years old)
--> No transmission slipping (it pulls like a train at full torque in all gears with no flaring)

.....

Troubleshooting performed so far:

A: Fluid / Filter change. All genuine parts/fluid, G 052 162 A2 fluid, which is rebranded Mobil LT 71141.
--> Immediately following the fluid change, it drove like silk, better than ever, with imperceptible changes, feeling more or less like a 1 speed box.
--> Gradually, the gear changes went back to perceptible (what I call "normal", you can feel it shift, but it's smoother than any manual)
--> The occasional slow 1-2 shift at 3.5K still happened occasionally

B: Replacement Valve Body, sourced from USA, overhauled with Sonnax parts (Central Valve Bodies)
--> This made matters worse, and was jolly expensive
--> The vehicle still had the occasional 1-2 delayed shift, but also gained a 3-4 flare shift where it would rev high and thud into 4th. Undrivable unless shifter is left in 3rd, ignoring 4th gear.

C: Light overhaul of original Valve Body (UK Firm, Valve Bodies UK)
--> Replaced the TCC lockup valve / sleeve / spring with no re-boring of VB
--> Machine dyno tested original VB, sent it back to me, in-spec by their judgement
--> Car shifted like silk once again after re-installing + new fluid (again)
--> 1-2 late shift initially improved seemingly, but has since resumed occasionally happening (the same 3.5K RPM late change)

D: Testing of electronic inputs to TCM according to Audi factory manual (Erwin)
--> All tested in spec except for the shift lock solenoid being a bit high on resistance (the solenoid that locks the lever in P/N, not a shift solenoid)
--> All shift solenoids are at correct and same resistance tested at both the solenoids themselves and at the TCM harness fully installed in the vehicle
--> Speed sensors both test in spec by resistance (but I'm aware that says nothing about magnetic pulse strength)
--> Nonetheless, no fault codes

E: TCM electronics -
--> I have replaced the main MOSFET power control transistor on the TCM mainboard, being the main power control component that can wear with heat/age.
--> This seems to have changed the shift behaviour for the better, but not fixed the occasional 1-2 slow 3.5K RPM shift.
--> Now the vehicle more readily downshifts when the throttle is pressed. I spend more time driving at <20% pedal for the same performance, and it more rarely needs manual intervention going up steep hills.

F: Cruise Control / Air Conditioning
--> Both these systems input to the TCM. Both work.
--> TCM binary output seems to indicate it is not aware of when the Cruise control is switched on. Nonetheless, C/C seems to work, cut out on brake / resume when told to/etc.
--> The A/C seems to cut out when the car is put in reverse. This seems odd. I know newer cars close the recirc flap on reverse, but I don't think this one is supposed to do this.
--> A/C correctly cuts out on kick-down. That's normal

......

For all that, I have yet to fix the occasional 1-2 slow shift at 3.5k RPM.

Questions for the forum:
1. Does this sound more electrical or mechanical to you? With the always exactly 3.5K RPM, my money is on electrical / logical, but I'm not sure where yet and more than happy to hear other suggestions...
2. Can anyone tell me where the grounding point is for the transmission harness? is it multi-point grounded? I've only found the ground points by the A pillars next to the doors behind the trim so far. I know the control logic depends on accurate consistent resistance on the harness, and it's a 26 year old harness now.
3. What parts would anyone change next?
Speed sensors, Solenoid ribbon, Replace TCM itself, Cruise module, A/C module, other electrical ideas?
4. Is the fact of "no codes" on a car of this era necessarily indicative of perfectly good electrics?
5. Would anyone still vote this being a valve body issue given the above (which was my initial thought)?

......

I'm hoping there is another 80K miles in the transmission before a rebuild...

Thanking anyone for reading this far!!

Kind Regards,

Jay.

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Automatic Transmission troubleshooting