My 2003 Dodge Durango is slipping when accelerating out of parking and I believe it's stuck in overdrive. The vehicle has error codes P1603, P1604, and P1698. I'm not sure what these codes mean or how to fix them. Can someone explain the root cause and provide a step-by-step solution? The truck is stock with no remote starter, and it's equipped with a 4.7L engine.
Yes, it's a fully stock setup. No remote starter is installed. The engine is a 4.7L V8.
That rules out common aftermarket causes. This issue will require a detailed wiring diagram — specifically for the PCM pinout and power circuits. Start with basic checks: verify that the transmission relay is energizing. Check all relevant fuses in both the cabin (fuses #18, #32, #34) and under the hood (#19, #22). These are essential first steps.
Definition: - P1603: PCM INTERNAL DUAL-PORT RAM COMMUNICATION FAILURE — detected during ignition off, on, and run/start conditions. Indicates an intermittent open circuit in the fused ignition switch output signal to the PCM. - P1604: PCM INTERNAL DUAL-PORT RAM READ/WRITE INTEGRITY FAILURE — also triggered during ignition cycles. Points to internal PCM failure or a faulty connection in the ignition switch output circuit.
I checked all fuses in the cabin, but #32 and #34 are missing. Fuse #18 controls interior lights. I have no blown fuses. What should I do to resolve P1603 and P1604? Will fixing these codes fix the overdrive slipping issue?
I’ll recheck the wiring diagram tomorrow — I was rushed reading it. For the transmission code P1698, check if the transmission relay is energizing. I’ll post the correct fuse numbers later. My mistake: I referenced a 2004 model’s fuse layout earlier — I’ll update with accurate info for a 2003 Durango.
I replaced the transmission relay, but the issue persists. I’ve also checked all fuses in both the cabin and under the hood — none are blown.
Could replacing the PCM with a used one from a junkyard solve this problem?
Junkyards sell used parts — but diagnosing a failed PCM requires more than just swapping. The issue is that the PCM isn’t receiving proper power on its circuits. This diagnosis needs a wiring diagram, PCM pinout, digital multimeter (DVOM), and an OBD2 scanner. These tools are necessary to test each circuit individually. I recommend checking not only the relay but also the full circuit path — including fuses and wire integrity — to ensure all connections are sound.
Surprisingly, I pulled a used PCM from a junkyard and it completely resolved the issue. The truck now shifts smoothly with full power and overdrive is working properly. Only minor issues remain — oil and ABS lights are on, but that may be unrelated.
Keep your original PCM — do not dispose of it. It may still be useful for future diagnostics or as a backup.
Now that I know the root cause, I’m going to purchase a remanufactured PCM from NAPA or Advanced Auto Parts tomorrow. Thanks for your help!
Try this before spending money: clear the codes and reinstall the original PCM. If the problem returns, it confirms that the issue lies with the PCM itself.
I cleared the codes and reinstalled the original PCM — the transmission started acting up again, losing overdrive and the shifter indicator light went out. Switching back to the junkyard PCM restored full functionality. The only remaining lights are oil and ABS, which may be unrelated.
Which engine model? These codes indicate PCM power or communication errors. There is a Technical Service Bulletin (TSB) for a reflash, but it's unlikely to work after 12 years. The P1698 code suggests the vehicle may be stock — let’s confirm that. Are there any aftermarket systems like a remote starter installed? Please provide more details so we can narrow down the diagnosis.