- Author: Mike Souza
Diagnosing code P1624 and/or P1121 in Kia Sephia
If a 1998 or newer Kia enters your shop with code P1624, MIL request signal from TCM to ECM, and/or P1121, TPS signal malfunction from ECM to TCM, here’s a new approach to diagnosing and solving the code.
Kia, like Hyundai, takes a DC-voltage signal from the TPS to the ECM and converts it to a pulse-width-modulated duty cycle. This signal then is sent to the TCM in a square-wave form. To diagnose this code and determine whether the circuit from the ECM to the TCM is working correctly, you must monitor the signal at the TCM with either a graphing meter or an oscilloscope.
Figure 1 is a section of a pin voltage chart for testing the TPS signal at the TCM as seen in a factory repair manual. As you can see, the chart identifies the pin on the ECM for which the TPS signal is sent. Figure 2 shows a wire schematic for the TPS-signal connection to the TCM by way of the ECM.
The chart in Figure 3 explains what the voltage readings should be at the ECM in comparison with the voltage at the TCM.
Figures 4 through 13 show the signal as displayed on a graphing meter or oscilloscope. You should view the signal in its square-waveform to truly see any glitches or dropouts. These figures also show the corresponding signal on a digital multimeter.
When I first read about this change, I found it really interesting and unusual that the TCM would receive a TPS signal in a square-wave form from an ECM. I wondered what it would look like and whether it was possible to read the signal with a digital multimeter. These are photos that I took of waveform signals and digital-multimeter readings at the TCM from a known good working 2000 Kia Sephia. I hope this may be helpful to someone as a guide.
During the writing of this article, I received a tech call for a 2000 Kia Sephia. The caller was getting the same code P1624 along with code P1500, no vehicle-speed signal to TCM. The speedometer/odometer in the instrument cluster was still functioning. I learned that the VSS signal from the transaxle is sent first to the instrument cluster, then to the ECM, TCM and cruise-control module, as the wire schematic in Figure 14 shows. The next approach would be to look for a VSS signal from the instrument cluster to the TCM.
I’m sure this is only the beginning of the tech calls we will be seeing in the near future on Kia and Hyundai models coming into the shop. Just remember there can be different ways for a computer to be looking for sensor signals that we’re just not used to seeing, so keep an open mind to the possibilities.
Mike Souza is a technical-hotline specialist with the Automatic Transmission Service Group (ATSG).