CAUTION: To prevent damage to connector terminals, DO NOT probe PCM connector terminals at very end of terminal. Instead, backprobe these terminals, even when PCM connector is disconnected.

Turn ignition on, with engine off. Using Scan Tool, monitor EVO SOLENOID - HIGH VOLT test, while turning EVO SOLENOID off. If test fails, go to next step. If test does not fail and DTC still exits, problem is intermittent.
Disconnect EVO solenoid. Connect jumper wire between high and low EVO PCM circuits (Brown & White wires). Using scan tool, monitor EVO SOLENOID - HIGH VOLT test, while turning EVO SOLENOID off. If test passes, check for tight connection at terminal. If test does not pass, go to next step.
Using DVOM, measure voltage on high EVO circuit (White wire), while turning EVO solenoid on. If voltage is not present, circuit No. 1876 is open, or terminal is too tight to PCM. If voltage is present, go to next step.
Connect test light between EVO low circuit (Brown wire) and battery positive terminal. If test light illuminates, EVO high circuit is shorted to voltage. If not, EVO low circuit is open or terminal connection is too tight.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

DTC P0637: High Circuit: Notes

Use the Manual With the Right Hardware

When to See a Mechanic

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