Jeep: Ambient temperature sensor engine light code, technical service bulletins, jeep wrangler

Question
I have a 99 4.oL jeep wrangler. the engine light code is 1493 (Ambient temperature sensor voltage too low). I am not sure if this is the oxygen sensor or not. what needs to be done?   Thank you

Answer
Ed,

Actually, 1493 is the Battery Temp Sensor Voltage High. Did you use the ignition off-on-off-on-off-on method for checking codes, or an aftermarket scanner? Sometimes, the code is displayed wrong with non-DRB3 scanners, so before the diagnostics, make sure of the code. The next step is to make sure the code is active before diagnosis, which normally involves battery disconnects, unless you have a scanner. However, due to the parameters of diagnostic codes, the light can be on and the code is inactive -- leading to misdiagnosis almost 100% of the time. After that, a quick perusal of the Technical Service Bulletins -- I've already done that, and none reference this issue directly.

This code seems very simple, particularly when it's actually the sister code -- 1492 -- which is voltage low (below .4v for 3 seconds). Most times, you can trace that to a chaffed wire to the battery sensor, both wires shorted together, or a failed sensor. This sensor is on the bottom of the battery tray, under the battery -- which is good and bad. Bad, because if the battery leaks, it fries the sensor, and good, because if the battery is leaking, you definitely want to know. Always inspect the battery when diagnosing this concern, as it can often reveal the cause of the failure.

Your code is the 1493 -- sensor voltage too high, which is above 4.9v for 3 seconds. Usually, any reading above 4.9v indicates an open circuit, which typically means a disconnected sensor, an open wire to the sensor, or a failed sensor. The diagnostics in the book calls for using a DRB3 for reading voltage values, and comparing them to actual values measured -- but I'm sure any scanner could do this.

Unless you have access to a scanner, and can use a multimeter, then I'd suggest taking it to a pro. As with all things electrical concerning the vehicle's computer, something simple can turn difficult in a short amount of time. Visual inspection is your best friend at this point -- if something *looks* wrong, then it probably is wrong. Good luck!