DTC C2194/94: Engine Speed Signal Error (Test Mode DTC): Procedure

1. Turn the ignition switch off.
2. Connect a Techstream to the DLC3.
3. Turn the ignition switch ON and the tester ON.
4. Enter the following menus: Chassis / Tire Pressure Monitor / Data List
5. Check that the values indicated on the tester and on the combination meter are the same.
   TIRE PRESSURE MONITOR
   
   

   Tester Display	Measurement Item/Range	Normal Condition	Diagnostic Note
   Engine Speed	Engine speed/ min.: 0 rpm max.: 65535 rpm	Almost same as actual engine speed	Speed indicated on combination meter

   OK

   Engine speed indicated on the tester and on the combination meter are the same.

NG → See step   2 

OK → See step   4 

1. Disconnect the E74 ECU connector.
   Fig 1: Inspecting Tire Pressure Warning ECU (Tach Signal) With Waveform Graph

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Start the engine.
3. Check the waveform of the ECU connector using an oscilloscope, while idling the engine.

   OK

   Tester Connection	Condition	Specified Condition
   E74-4 (TACH) - E74-9 (GND)	Idling	Correct waveform is as shown

   TOOL SETTING
   
   

   Item	Contents
   Tool Setting	5 V/DIV., 10 ms/DIV.

   HINT: 

   The wavelength becomes shorter as the engine speed increases.

NG → See step   3 

OK → See step   5 

1. Disconnect the E74 ECU connector.
2. Disconnect the E77 ECM connector.
3. Measure the resistance according to the value(s) in the table below.

   Standard resistance

   Tester Connection	Condition	Specified Condition
   E74-4 (TACH) - E77-29 (TACH)	Always	Below 1 Ω
   E74-4 (TACH) - Body ground	Always	10 kΩ or higher

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

OK → See step   6