P0740 & P1687 Fault Codes on 2004 Jeep Grand Cherokee Limited with 4.7L V8 - Diagnosis and Repair Tips
I've been experiencing persistent check engine light issues on my 2004 Jeep Grand Cherokee Limited with a 4.7L V6 engine, showing fault codes P0740 and P1687. Using my OBD2 scanner initially, I detected P0740; however, when I took it to AutoZone, they reported both P0740 and P1687. The check engine light sometimes doesn't illuminate until after driving 10–15 minutes. While the vehicle generally drives smoothly for a while, it eventually begins running roughly with significantly reduced fuel efficiency. The transmission fluid appears clean and has no unusual odor, but I recently purchased this vehicle and was advised that using ATF+4 or performing a transmission fluid flush might resolve underlying issues. As a result, I'm considering adding one quart of Lucas Transmission Fix to the system and am wondering if this could help. In addition, are there any specific solenoids, sensors, or control modules I should inspect? I also checked several fuses under the hood (fuses #5, 17, 19, 22, 28, and 31) related to the TCM, ECM, PCM, and instrument cluster, as well as those under the dash (#17 and #23), including the instrument cluster diagnosis connector and brake switch. I found that about one-third of these fuses are empty or missing — is this normal for a 2004 Jeep Grand Cherokee Limited? Any advice on diagnosing or fixing these issues would be greatly appreciated. I'm hoping I didn't buy a lemon, but I'd like to understand what's really going on before making further investments.
P0740 indicates a torque converter clutch (TCC) issue — specifically, no RPM drop at lockup. This could point to several potential causes: misfire codes, intermittent TCC solenoid failure, low transmission fluid level or poor condition, input shaft seals, internal transmission problems, oil pump or shaft issues, torque converter malfunction, valve body defects, or a failing TCC solenoid. P1687 indicates no communication from the Mechanical Instrument Cluster (MIC) module — meaning the instrument cluster is not receiving data from the vehicle's bus system. This can result in incorrect gauge readings and may be linked to faulty wiring, a failed MIC module, or issues with the PCM communicating with the cluster. Recommended steps: Check for misfire codes first; inspect transmission fluid level and condition; verify TCC solenoid operation; ensure proper electrical connections to the instrument cluster; and confirm that the PCM is sending signals properly to the cluster.