![]() ![]() With GMs 4L80-E transmission, this code has usually been the resuit of a cracked converter clutch piston. Fortunately, experience has shown that in most cases, the cause can be traced to some form of converter clutch failure as a result of valve body concerns. If the ratio breaks away, the cause could be any of three components, the hydraulics that operate them or the electronics that control them. When it's in Overdrive, the forward clutch and the 3-4 clutches are applied, as well as the 2-4 band. Take a GM 4L60-E transmission, for example. When this code sets, it could have any number of causes, ranging from the sump running low of fluid to a malfunctioning torque converter. ![]() This would explain why DTC 1870 Ls often accompanied by a complaint of a hard 1-2 upshift. If at some point the transmission begins to slip, P1870 sets and line pressure is elevated in an attempt to stop any further slippage and prevent further damage. Once the vehicle has made it to a cruise state, the PCM then begins to monitor the vehicle's cruise ratio. This really is an added safety strategy, as the PCM had already monitored the upshifts and determined all was well through those ranges. In some instances, the PCM also will inhibit 4th gear and may or may not illuminate the MIL. And upon doing so, the PCM elevates the transmission main line pressure and stops converter clutch apply. Should the expected rpm ratio exceed predetermined parameters, DTC 1870 sets. The PCM monitors and compares engine speed to vehicle speed after the converter clutch has been commanded ON in either high gear or Overdrive. As is often the case, an appreciation of how it works will help you understand why if something goes wrong.ĭiagnostic trouble code P1870 (Transmission Component Slippage) is a General Motors-specific code whose set parameters are determined by transmission type and engine size. The newest transmission technology provides nearly unnoticeable torque converter clutch application. Slip-Sliding Away: Deciphering GM Transmission DTC P1870 Here's the text, but it's better in the PDF with illustrations: Here's the page for the magazine issue where that article was published:įrom there you can view articles available from that issue or go to pages for other issues. They've probably got a bunch of great articles like that. They use the GM 4L60E as their example, and follow it over the years of changes in TCC solenoid control / clutch material. It's a detailed explanation about how PWM-controlled TCCs work. I found this great fully illustrated PDF: ![]()
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