ECM Code EO28: Open 3RD Or 4TH Gear Circuit: Action:
ECM turns on SERVICE ENGINE SOON light. The 3rd and 4th gear (transmission) switches are normally closed switches that open with transmission oil pressure. The ECM sends a 12-volt signal to each switch. When not in 3rd or 4th gear, 3rd and 4th gear inputs are grounded by normally closed switches. When in 3rd gear, 3rd gear switch is opened by oil pressure and input changes from zero to 12 volts. When in 4th gear, 4th gear switch is opened by oil pressure and input changes from zero to 12 volts. Code EO28 detects false 3rd or 4th gear indication to ECM.