P0904Generic code

P0904 Code: Gate Select Position Circuit

The P0904 code means there is an electrical fault in the gate select position sensor circuit. The main effect is that the transmission does not know where its mechanism is. Test the connector, wiring and reference voltage before you replace the sensor.

Severity
High
Can I keep driving?
Yes, but with caution
Estimated cost
$60 to $800
Difficulty
Medium
System
Transmission
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0904 code means

Automated manual transmissions (Opel Easytronic, Fiat Dualogic, Toyota MMT, BMW SMG, Ford Durashift, Volkswagen ASG) and many dual clutch transmissions use electric or hydraulic actuators to disengage the clutch, to choose the gear plane (select) and to engage the gear (shift). The transmission computer watches every actuator with position sensors. The select sensor reports which plane the mechanism is in.

The sensor gets a 5 volt reference and a ground from the computer and sends back a signal between about 0.5 and 4.5 volts. The P0904 code is set when the circuit has a fault, which may come from the sensor, the wiring or the supply.

If its signal fails, the computer does not know which plane is selected and blocks the shifts. After any repair of these components you must run the transmission relearn procedures with a scan tool (clutch touch point, select and shift positions). Without them the transmission will not work properly.

Always start with the simple things: the fuse, the relay and the connector. Then check supply, ground and signal with the component connected, using back probes, and finally the continuity of each wire to the computer. Only if all of that is good should you replace the component.

P0904 code symptoms

  • Check engine light on.
  • The transmission does not recognize the position of its mechanism.
  • The transmission does not go into gear or stays in neutral.

Likely causes of the P0904 code

  1. Damaged or corroded connector. The most frequent cause.
  2. Wiring cut or shorted between the sensor and the computer.
  3. Failed sensor, open or internally shorted.
  4. Missing reference supply. Check whether other sensors are also failing.
  5. Computer. Uncommon, so rule out everything above first.

How to diagnose the P0904 code step by step

  1. Read the sensor value on the scan tool and compare it with what you expect.
  2. Inspect the connector for corrosion, water or loose pins.
  3. Check supply and ground with the key on: the reference should be correct and the ground voltage drop under 0.1 volts.
  4. Measure the signal with the connector attached and see whether it changes with the condition.
  5. Do a wiring wiggle test with the scan tool in graphing mode.
  6. Check the continuity of each wire to the computer (under 1 ohm).
  7. Run the transmission relearn procedures after the repair.

How to fix the P0904 code

  • Repair the connector or the wiring.
  • Replace the sensor if the tests confirm it is bad.
  • Correct the real condition if one exists.
  • Clear the codes and verify with a road test.

Technical reference data

  • 5 volt reference, ground and a signal of 0.5 to 4.5 volts (or a contactless Hall effect sensor).
  • Approximate values only: check the manufacturer data for your vehicle.

Brand-specific notes

This code is very common on automated manual transmissions. On many hydraulic systems the actuator fluid is a specific type and the reservoir should be checked regularly.

P0904 on Opel

Very common on the Opel Easytronic.

P0904 on Fiat

Very common on the Fiat Dualogic.

P0904 on Toyota

Very common on the Toyota MMT.

P0904 on Smart

Seen on Smart vehicles with an automated manual transmission.

P0904 on BMW

Very common on the BMW SMG.

Frequently asked questions about P0904

Can I drive with a P0904 code?
With caution. The transmission can be left without gears.
Do I have to replace the sensor?
Only if the tests confirm it. The connector and the wiring fail just as often as the sensor does.
What does the gate select position sensor do?
Automated manual transmissions (Opel Easytronic, Fiat Dualogic, Toyota MMT, BMW SMG, Ford Durashift, Volkswagen ASG) and many dual clutch units use electric or hydraulic actuators to release the clutch, select the gear plane and engage the gear. The computer watches each actuator with position sensors. The select sensor reports which plane the mechanism is in.
How much does it cost to fix P0904?
As a rough guide, between $60 and $800. A connector or wire repair is at the low end, and a new sensor with the relearn procedures costs more.
What does the P0904 code mean?
The P0904 code is a generic OBD2 code that means there is an electrical fault in the circuit of the sensor that reports the gate select position.
Will a P0904 code clear itself?
Only if the cause was a temporary glitch. A damaged connector or a failing sensor will bring it back.
What is the most common cause of P0904?
A damaged or corroded connector. Cut or shorted wiring and a failed sensor follow.

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