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If you’re swapping in a 3.4 engine and ECU from a vehicle with an automatic transmission into a vehicle with a manual transmission, the ECU will be expecting signals from the automatic transmission solenoids. If it doesn’t see those signals, it will illuminate the check engine light (CEL), also called a malfunction indicator lamp (MIL). To avoid that, the signals can be spoofed or simulated using resistors. If you know how to use a soldering iron, then this is a pretty simple DIY project to simulate the automatic transmission solenoids.
Parts Needed
- (3) 15 ohm power resistor, rated for 25 W or higher (Buy on Amazon)
- (1) 5 ohm power resistor, rated for 50 W or higher (Buy on Amazon)
- 18–20 AWG wire
- Project box or mounting surface
Tools Needed
- Wire cutters/strippers
- Soldering iron
- Solder
Pinout
A 3rd generation auto ECU will have 5 pins for the Electronically Controlled Transmission (ECT) Solenoid. In a 2002 4Runner, these pins are as follows:
- SL (Connector E9 Pin 1, LG)
- S1 (Connector E9 Pin 3, P-L)
- S2 (Connector E9 Pin 2, L-W)
- SLT+ (Connector E11 Pin 5, R-Y)
- SLT- (Connector E11 Pin 11, Y-B)
The SL, S1, and S2 wires all go through the solenoids to ground. The SLT+ wire goes through the solenoid and back to the ECU to the SLT- pin.
You will need to look at the Electronic Wiring Diagram (EWD) for your 3.4 engine’s model year and confirm the ECU pin locations and wire colors, because they will vary by year.
Spoofing the Solenoids
Each solenoid has a range of resistance and voltage that the computer expects to see.
The SL, No. 1, and No. 2 solenoids all have a resistance of 11–15 ohms, and range in voltage from < 1.5 V to 9–14 V, depending on which gear the auto transmission is currently in. Using the formula I = V / R, we can therefore calculate the maximum wattage as 14 V / 11 ohms = 17.8 W. To be safe, we’ll want to be able to safely dissipate 25 W of power.
The SLT solenoid has a resistance of 5.0–5.6 ohms, and pulses between < 1.5 V and 10–12 V when the engine is idling. Consequently, we can calculate the maximum wattage as 12 V / 5 ohms = 28.8 W. We can round this up to safely dissipate 50 W of power.
Based on this information, we can use 3 power resistors rated for 15 ohms and 25 W to simulate the SL, No. 1, and No. 2 solenoids, and we can use 1 resistor rated for 5 ohms and 50 W in place of the SLT solenoid. These finned, aluminum power resistors do a good job dissipating heat and work well for this application:
Higher power ratings will only help dissipate heat better, so you can size these up if you’d like. We used 100 W resistors for all 4 the first time we built this.
Building the Simulator
Essentially all that needs to be done is soldering wires to the resistors, and connecting the wires to the ECU and ground accordingly. Using the solenoid diagram from the EWD, lay out the resistors, cut wires to length and strip them, and solder them to the resistors.
The wires to the ECU connectors ideally should be joined with a lineman splice to the connector wires and then soldered. This will create a very strong connection to avoid signal interruption to the ECU. Optionally, instead of a direct splice, the wires can be crimped and soldered to terminals or a multi-pin connector, so that the simulator can be easily removed from the ECU later.
There are 2 options for the ground wire coming from 3 of the resistors:
- Run it directly to a bolt on the chassis for a direct ground
- Splice it into the ground wire coming from the ECU
Testing the Simulator
Once everything is wired up and the simulator is connected to the ECU and properly grounded, then you should no longer have DTCs (Diagnostic Trouble Codes) related to the automatic transmission solenoids. If these were the only codes causing your CEL to illuminate, then you should no longer see the CEL when the ignition is on!