How To Diagnose A Cel Without A Scanner Tool

[godpossessed]

My '91 LS400 has 191K miles. Ever since I replaced the fan bracket it has gotten 2-3 miles to the gallon less than before. I recently left the cap off the radiator remote tank and didn't find it until today. I was about 30 minutes into a short trip when I got a check engine light. When I stopped to investigate the CEL, I found the cap off and put it back on. I completed the trip, replaced the lost water and on the way home the CEL went off. Question: How do you make the computer tell you what's wrong (without a scan tool)? Maybe the CEL is unrelated to the radiator cap issue but might tell me about the missing gas mileage.

thanks

Mark

[pishta]

My '91 LS400 has 191K miles. Ever since I replaced the fan bracket it has gotten 2-3 miles to the gallon less than before. I recently left the cap off the radiator remote tank and didn't find it until today. I was about 30 minutes into a short trip when I got a check engine light. When I stopped to investigate the CEL, I found the cap off and put it back on. I completed the trip, replaced the lost water and on the way home the CEL went off. Question: How do you make the computer tell you what's wrong (without a scan tool)? Maybe the CEL is unrelated to the radiator cap issue but might tell me about the missing gas mileage.

thanks

Mark

95-96 and newer used the OBD2 diagnostic computer that shows codes via scan tool, its a generic coupler across the board so codes can be read by any OBD2 scan tool. Before these were proprietary interfaces and the computer would either show codes on its own proprietary reader or flash codes after a jumper is inserted into 2 sockets of the plug. 91 LS400 will flash codes when jumped by flashing the CEL in a morse code type fashion, counted flashes, a pause and then a second set of counted flashes, like 123...1234........123...1234....that would tell you you had a code 34 stored or active, then you look up code 34 in this forum and itll say something like "downstream 02 r side malfunction" or whatever.

[godpossessed]

My '91 LS400 has 191K miles. Ever since I replaced the fan bracket it has gotten 2-3 miles to the gallon less than before. I recently left the cap off the radiator remote tank and didn't find it until today. I was about 30 minutes into a short trip when I got a check engine light. When I stopped to investigate the CEL, I found the cap off and put it back on. I completed the trip, replaced the lost water and on the way home the CEL went off. Question: How do you make the computer tell you what's wrong (without a scan tool)? Maybe the CEL is unrelated to the radiator cap issue but might tell me about the missing gas mileage.

thanks

Mark

95-96 and newer used the OBD2 diagnostic computer that shows codes via scan tool, its a generic coupler across the board so codes can be read by any OBD2 scan tool. Before these were proprietary interfaces and the computer would either show codes on its own proprietary reader or flash codes after a jumper is inserted into 2 sockets of the plug. 91 LS400 will flash codes when jumped by flashing the CEL in a morse code type fashion, counted flashes, a pause and then a second set of counted flashes, like 123...1234........123...1234....that would tell you you had a code 34 stored or active, then you look up code 34 in this forum and itll say something like "downstream 02 r side malfunction" or whatever.

Excellent - is there a resource that describes the procedure and identifies where the jumper should be attached?

thanks

m

[aarman4]

http://www.lexls.com/tutorials/intro/codereading.html

While your there, check out "tutorials" at the top of the page as well and it will show you how to do almost everything to your lexus!

Best of luck, there is also a code listing on the last half of this lesson.