P0700 & P1870 Code on 1998 S-10 4x4 Automatic: Possible Transfer Case Switch Issue
I own a 1998 Chevrolet S-10 4.3L V6, 4x4 automatic transmission. I've had it for about a year and have been consistently receiving the P1870 code (and associated P0700 code) since purchase. I've cleared the codes multiple times by disconnecting the battery, but they return within 5 to 7 miles of driving. The truck originally had 113,000 miles and has accumulated approximately 12,000 miles since. It has performed well overall—no noticeable slipping, smooth shifts between gears, and no harsh 1-2 shift behavior. However, I've recently observed that the transfer case switch occasionally fails to illuminate the 2H light when engaging 4WD, and once it was slow to disengage from 4WD. The P0700 code is broad in scope but has been linked to potential issues such as component slippage, faulty transfer case shift components, a worn or malfunctioning TCC (torque converter clutch) circuit/valve body (which typically causes harsh shifts), or degraded transmission fluid. I haven't flushed the fluid yet, though it appears clean and smells normal. Given that the code appears without any 4WD engagement attempts, I suspect the issue may be with the transfer case encoder motor—a component known to be costly and difficult to replace. However, before investing in a replacement, I'd like to get expert input on whether this is likely or if another diagnosis (such as a faulty transfer case control switch) might be more probable. I no longer have access to a Tec-II scanner for detailed diagnostics, and since I'm planning to sell the vehicle, I want to avoid unnecessary diagnostic costs. Any insights would be greatly appreciated.
I recently had a similar issue with my 2002 Chevrolet Silverado 5.3L 4x4 automatic. The Engine Management System displayed a 'Service Transfer Case Soon' message, which only occurred when the 2H light on the transfer case control switch (located in the dash) was not illuminated. No drivability or performance problems were present during these instances. After pulling the diagnostic code (I no longer recall the exact code), I found it was related to a faulty transfer case control switch. Replacing the switch resolved the issue completely. To obtain the correct replacement part from the dealer, I had to provide my VIN number. Based on my experience, I believe your transfer case control switch may be defective and could be triggering both the P0700 and P1870 codes. This is especially plausible given that the symptoms occur without 4WD engagement attempts. I should note that the new switch cost me $130 CDN. I hope this helps—good luck, and please keep us updated on your findings.