Troubleshooting — symptom to cause

Start here when the car does something wrong. This page is organised by what you observe, not by fault code — look up the code afterwards in Fault codes and Fault diagnostics.

Before anything else

Three checks resolve a large share of problems and cost two minutes:

  1. Read the fault list. Most faults name the exact element that is wrong. How to read and clear faults.
  2. Check every mandatory input and output is assigned. A gateway checks these at startup and refuses to run if one is missing — 8HP · PDK.
  3. Check the engine torque value is sane. It sets clutch pressure, nothing validates it, and no fault is raised when it is wrong — ten-minute check.

Quick reference

Symptom Most likely causes Start with
Won't come out of Park, or won't engage a gear Mandatory input or output unassigned; shifter not read; brake signal missing ↓
Limp home, or locked in one gear TCU fault; implausible speed or torque signal; CAN dropout mid-drive ↓
No upshift above a certain gear Speed signal wrong or missing; torque reading high; TCU never sees the conditions for the shift ↓
Harsh or slipping 1–2 shift Torque estimate wrong; adaptations learned against a bad signal ↓
Shifts fine on the bench, badly in the car Signals that were static on the bench are now live and wrong — load, speed, torque ↓
Gear display wrong or blank Gear output not routed, or scaled wrong at the consumer ↓
No CAN traffic at all KL15 missing, wrong bus wired, baud mismatch, termination ↓
Transmission wakes then immediately sleeps Wake-up output not routed; ignition input unassigned; supply collapsing under load ↓
Reverse unavailable Shifter state not reaching the driver; brake interlock; TCU refusing on a fault ↓
Shift quality degrades when hot Adaptation limited by temperature; genuine hydraulic or clutch wear; torque error that only shows under heat ↓
Adaptations keep resetting between drives Supply cut with the ignition, so the save never completes ↓

Won't come out of Park, or won't engage a gear

This is almost always a configuration fault, not a transmission problem.

Check Detail
Mandatory inputs all assigned? The gateway drivers check these at startup and fault if any is missing. The 8HP gateway requires seven; the PDK gateway requires eight — vehicle speed is mandatory on PDK but not on 8HP, which catches people porting a configuration between them
Mandatory outputs all assigned? Thirteen outputs are checked the same way. An unassigned one faults exactly like a missing input, and this surprises people who assume outputs are optional
Brake signal present and toggling? Mandatory on both gateways, and absent from several aftermarket ECU streams — the Ecumaster EMU Black carries no brake signal at all, so it must come from an analog channel or a device input
Shifter reaching the driver? Check the shifter's decoded position in the datalogger, not the lever. See the shifter pages

The fault raised for an unassigned element names the element — read the fault list first and you will usually not need this table.

Limp home, or locked in one gear

The TCU has decided it cannot shift safely. It is reporting a decision, not a defect in itself.

Check Detail
TCU faults Read them over the diagnostic path. A TCU in limp home usually has a stored reason
Speed plausibility The gateway cross-checks the TCU's tailshaft speed against the vehicle speed input and warns when they disagree by more than ~10 %. A wrong diff ratio or wheel diameter produces exactly this — see Vehicle & wheel speed
Torque signal A wildly wrong torque value can drive the TCU into protection. Check it
CAN dropout mid-drive If a signal stopped arriving, what the device does depends on that input's timeout mode, not on the driver. UsePrevious holds a stale value forever, which is the dangerous setting on anything safety-relevant — see If an input drops out

No upshift above a certain gear

The TCU schedules shifts from speed and load. If it never sees the conditions, it never shifts.

Check Detail
Speed signal Verify road speed against GPS. If it is off by a constant factor, revisit diff ratio and wheel diameter — the shift schedule is built on this
Torque reading high An over-reported torque makes the TCU behave as if the car is under far more load than it is
Throttle and pedal position Both are mandatory inputs. Confirm they reach full scale, not just that they move
A ratio the transmission does not have Confirm the variant actually has the gear you are expecting — see the supported-variants page for your transmission

Harsh or slipping 1–2 shift

Check Detail
Torque estimate Harsh = reading high, slipping = reading low. This is the first thing to test: ten-minute check
Adaptations learned against a bad signal Corrections learned while the torque value was wrong stay learned after you fix it. Reset adaptations after changing the torque method or its calibration
Cut request not acted on On a gateway the ECU performs the torque cut; the gateway only sends a percentage request. If the ECU ignores it, the transmission still shifts but quality suffers — see Executing cut and blip in your ECU

Adaptations keep resetting between drives

Shift quality is good by the end of a drive and poor again at the next start, as though the transmission has been reset. On a standalone controller the usual cause is not the transmission at all — it is the supply.

Check Detail
KL30 and KL15 on the same switched source The controller saves its state after the ignition drops. If the supply drops at the same instant, the write never completes and the stored data can be corrupted rather than just stale
No off-delay on the supply KL30 needs to be held for about 60 seconds after the ignition goes off — advisory
KL30 wired to permanent battery instead This does give the controller its save window, but it has no low-power sleep mode — with KL30 present it keeps drawing 200–300 mA and will flatten the battery in hours. Use a time-delay-off relay

Full detail, including the relay part number and the current firmware status: Adaptation data lost when the supply drops with the ignition. The advisories index lists every known condition of this kind.

Intermittent is normal for this: the save only fails when it is still in progress as the supply collapses, so it can take many ignition cycles before the damage is obvious.

Shifts fine on the bench, badly in the car

On the bench, signals that are static or absent look harmless. In the car they are live, and wrong ones now matter.

Check Detail
Torque is now real On the bench there was no load, so a broken torque model was invisible. This is the most common answer to this symptom
Speed signals are now moving A diff ratio or wheel diameter error does nothing at standstill and everything on the road
Unassigned inputs were substituted Inputs that were never assigned get a fixed internal value rather than failing — intake air temperature 25 °C, atmospheric pressure 100 kPa, and so on. Harmless on a bench, wrong in a car
Bus load and termination A two-node bench bus is forgiving. A full vehicle bus is not — CAN diagnostics

Gear display wrong or blank

Usually a plumbing problem, not a transmission one.

Check Detail
Is the gear output assigned? Current gear is a mandatory output — if it is unassigned the driver faults
Scaling at the consumer The device's value and the dash's expected encoding must agree. The Ecumaster ADU page shows a worked example of the channel mapping
Park reported separately Current gear (Park) is its own mandatory output — a display that shows every gear except P is usually missing this

No CAN traffic at all

Check Detail
KL15 The device needs ignition to activate CAN. A missing KL15 wire looks exactly like a dead bus
Right bus wired? With four buses it is easy to configure one and wire another. Match the pins to the configured channel — pinout
Baud rate One node at the wrong rate does not just stay silent, it destroys traffic for everyone
Termination Exactly two 120 Ω terminators, one at each end — ~60 Ω across the pair with the power off
Nobody to acknowledge A lone node cannot complete a transmission. "My device doesn't transmit" is very often "nobody ACKs"

Full procedure, organised by what tools you have: CAN Bus Diagnostics.

Transmission wakes then immediately sleeps

Check Detail
Wake-up output routed? The device supplies transmission power and wake-up itself — no external relay — but the wake-up output has to be assigned
Ignition input assigned? Without it the device does not know the car is on
Supply collapsing under load With a full valve body and the engine off, current through the device should not exceed roughly 2 A. Much more than that, or a supply that sags when the transmission wakes, points at wiring or a marginal bench supply

Reverse unavailable

Check Detail
Shifter state Confirm the decoded shifter position in the datalogger shows R, not just that the lever moved
Brake interlock Many selectors require brake pressed to leave Park or select R. The brake signal is mandatory and is missing from several ECU streams
Reverse light output A mandatory output, and a useful confirmation that the driver believes it is in reverse
TCU refusing If the TCU has a stored fault it may withhold reverse specifically. Read its fault memory

Shift quality degrades when hot

Check Detail
Adaptation is temperature-limited Adaptation is restricted by transmission temperature by design, so a gearbox that never reaches temperature — or runs too hot — will not adapt correctly
Torque error that only appears hot An air-model estimate drifts with intake air temperature; a fuel-model estimate drifts with injector dead time at temperature
Genuine hydraulic condition Falling line pressure when hot is a mechanical symptom. If the electrical picture checks out, this is a transmission problem, not a configuration one

Still stuck — what to send us

Email contact@apex-control.com and include all of the following. Without them the first reply is always a request for them:

  • The fault list, read in the same power session as the problem — faults are not stored across power cycles
  • A datalogger capture covering the symptom, including engine torque, road speed, gear, and the mandatory inputs
  • Your configuration file
  • The firmware version on the device
  • What the car is: engine, ECU, transmission variant, shifter