← Back to list

2002 Dodge Ram 1500 OBD2 Code P1685: Remote Starter Not Factory Installed and Transmission Issues Explained

Model: 2002 DODGE RAM Fault Code: P1685 Posted: 2007-07-29 10:56

Hi everyone, I'm new to this forum and have a 2002 Dodge Ram Quad Cab 1500 4x4 with a 5.9L V8 engine. After taking my truck to the dealership for diagnostics, they identified OBD2 fault code P1685: 'SKIM INVALID KEY'. They explained that this code is triggered because remote start systems were not factory-installed in my model year. Since Dodge did not offer a factory remote starter for the 2002 Ram 1500, the system detects it as non-compliant and logs P1685. My main concern is: what impact does this code have on daily driving? Does it affect engine performance, fuel efficiency, or safety? Additionally, I've noticed that when using cruise control, my RPM gauge spikes by 200–300 RPM every 15 minutes, and the shifting feels slightly rough. When I purchased the truck in December 2005, only the transmission fluid was changed — not the filter. Could a clogged or worn transmission filter be contributing to these symptoms? I'm looking for reliable insights on both the P1685 code and potential transmission-related causes. Any advice would be greatly appreciated.

Related fault codes
P1685
Comments (4)
Anonymous 2007-07-30 08:54

P1685 is a known issue with aftermarket remote starters not being factory-approved. If the system detects an unauthorized or non-compliant remote starter, it may prevent the truck from starting and could lock out key programming — meaning you might lose access to your vehicle if you misplace or lose the original key. I recommend removing any aftermarket remote starter entirely. Once removed, the P1685 code should clear. Aftermarket systems often cause more problems than they solve. As for transmission issues, a faulty throttle position sensor is common when cruise control is active — it can trigger RPM spikes and rough shifting without throwing an obvious DTC. A full transmission service with proper filter replacement is strongly advised to resolve this.

Anonymous 2007-08-01 15:30

I’ve confirmed the dealership’s diagnosis. The remote starter will be removed as recommended. Once it's taken out, the P1685 code should disappear. Thanks for validating my concerns — I appreciate the clarity. I have an appointment scheduled on August 6, 2007, and I’m hopeful that the transmission issue can be resolved without major repairs.

Anonymous 2007-08-11 00:27

After returning from service, I found out my issue was a faulty Throttle Position Sensor. The dealer initially suggested replacing it — it cost me $200 including parts and labor. If I had done the repair myself after learning about the problem, I could have saved around $150. Since the issue was already diagnosed, I’m glad with the outcome. My truck now runs smoothly with no RPM spikes or shifting roughness. Thanks for the helpful advice — it made a big difference in my troubleshooting process.

Anonymous 2007-08-11 07:14

I’ve seen similar issues with multiple trucks and have had to replace various sensors and components every few weeks — especially when dealing with cruise control and remote start systems. This highlights how aftermarket modifications can introduce persistent, hard-to-diagnose problems.