Rick's Free Auto Repair Advice

Subaru P2138

Diagnose and fix Subaru P2138 trouble code

The Subaru P2138 THROTTLE/PEDAL POSITION SENSOR/SWITCH “D”/”E” VOLTAGE CORRELATION is a fairly common trouble code. It’s most often a bad throttle/pedal position sensor. But you check for the presence of carbon buildup in the throttle body first. If you find lots of carbon, remove the throttle body and clean it. Do NOT spray throttle body cleaner directly onto the throttle plate. That can wick into the electronics and damage them. Instead, apply cleaner to a shop rag and wipe off the carbon. should test it first to confirm. If you’ve cleaned the throttle body and still have the Subaru P2138 trouble code, conduct these tests

Subaru P2138 circuit tests

1) Check the connector at the throttle/pedal to make sure

subaru throttle wiring diagram

Subaru throttle/pedal wiring diagram

it’s securely connected. If so, proceed with these circuit tests.

2) Using a digital multimeter, back probe terminals 3 (Green/black) and 1 (White/blue). You should see a 5-volt reference voltage (key in RUN position). If not, check the circuit back to ECM

3) Backprobe terminals 4 (Blue) and 6 (Black/white) for ground. You should see less than 0.05 volts voltage drop. If you see higher voltage, check for bad ground connections.

4) Next, remove the connector from the throttle/pedal and check resistance readings across terminals 3 (Green/black) and 4 (Blue). The reading should be 1200-Ω to 4800-Ω.

5) Check the resistance readings across terminals 1 (White/blue) and 6 (Black/white).

6) With the connector still unplugged, fully depress the pedal and check the resistance readings between terminals 4 (Blue) and 5 (Black). The reading should be 500-Ω to 2500-Ω. Then check the resistance across terminals 2 (Red) and 6 (Black/white). You should see 280-Ω to 1680-Ω

7) Release the pedal and check the resistance values again. Terminals 4 (Blue) and 5 (Black) should read 200-Ω to 800-Ω. Resistance across terminals 2 (Red) and 6 (Black/white) should read 150-Ω to 630-Ω

If the readings aren’t in spec, replace the throttle/pedal.

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Posted on by Rick Muscoplat

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