While some older vehicles might have had rudimentary methods involving blinking lights or jumpers, the 2003 Jeep Liberty's system requires a scan tool to interpret the stored codes. Any attempt to decipher codes without a proper tool will likely be inaccurate and unproductive.
To read the codes, you need either:
* An OBD-II scanner: This is the most reliable and recommended method. Affordable generic scanners are readily available online and at auto parts stores.
* A more advanced scan tool: Some more professional-level scan tools offer more detailed information and capabilities beyond basic code reading.
Trying to find alternative methods will likely waste time and effort. Investing in a relatively inexpensive OBD-II scanner is the only practical solution.
