Didn't find anything the says what system your '91 is useing. You can retrieving codes from EEC-IV, but not an EEC-V without a scan tool. Haynes has a techbook that can help you retrieve codes, do a KERO test, and engine running codes. Sorry but '91 was one of those change over years, so the book may not help if its a EEC-V. EEC-IV 2-digit codes (91 and earlier models) code 41 is EGO sensor indicates system lean. So the sensor may just be reading 0.0V, open connector, or computer bad. [:'(]

 

HUMMM , ODD , I know all the Autozone's here local will check codes for you, ( trying to sell you parts ), Well the DTC ports are totally different , You couldnt get one to plug in the other if you tried , , Your tester did it come with several adapters ?,,, It should tell you under the hood the sticker that has your tuneup spec;s what system you got, It will say , ECC-IV, or ECC-V

 

Ok, looked up on the web, Innova 3145 , say for OBD1, which should be EEC-IV,,, where you plug the tester in , theres a small , single wire pigtail , that you gotta plug in the tester along with the main connector on the car , Right ??

 

Thanks for all of the responses Was able to make the code reader work. Had a loose wire in the dtc. The KOEO test receives a 41C-NO HEGO sensor switching. The KOER test receives the following codes: 42R-HEGO always rich; 72R-MAP, MAF or BP out of range; and a 73R-Insufficient throttle response. Additionally, the engines idles smoothly, has sufficient power, but uses an abnormal amout of fuel. Also, at idle the engine pulls a steady 22 inches of vacum. I have replaced the O2 sensor, mass airflow sensor, inlet air temp. sensor. engine coolant temp. sensor, pcv valve, oil & filter, and the air cleaner element. Tested the CNAP solenoid and the throttle position sensor. Plan to test the O2 sensor and circuit with a multimeter tomorrow. Thanks again.