Lexus NX: Vehicle Speed Signal Circuit between Navigation ECU and Combination Meter
DESCRIPTION
The navigation ECU receives a vehicle speed signal from the combination meter assembly.
HINT:
- A voltage of 12 V or 5 V is output from each ECU and then input to the combination meter assembly. The signal is changed to a pulse signal at the transistor in the combination meter assembly. Each ECU controls its respective systems based on this pulse signal.
- If a short occurs in any of the ECUs or in the wire harness connected to an ECU, all systems in the diagram below will not operate normally.
WIRING DIAGRAM
PROCEDURE
| 1. | CHECK COMBINATION METER ASSEMBLY (OUTPUT WAVEFORM) |
| (a) Check the output waveform. (1) Remove the combination meter assembly with the connector still connected. (2) Connect an oscilloscope to terminal I10-19 (+S) and body ground. (3) Turn the power switch on (IG). (4) Turn a wheel slowly. (5) Check the signal waveform according to the condition(s) in the table below.
OK: The waveform is similar to that shown in the illustration. HINT: When the system is functioning normally, one wheel revolution generates 4 pulses. As the vehicle speed increases, the width indicated by (A) in the illustration narrows. |
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| NG | .gif) | GO TO METER / GAUGE SYSTEM |
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| 2. | CHECK HARNESS AND CONNECTOR (NAVIGATION ECU - COMBINATION METER ASSEMBLY) |
(a) Disconnect the I173 navigation ECU connector.
(b) Disconnect the I10 combination meter assembly connector.
(c) Measure the resistance according to the value(s) in the table below.
Standard Resistance:
| Tester Connection | Condition | Specified Condition |
|---|---|---|
| I173-9 (SPD) - I10-9 (+S) | Always | Below 1 Ω |
| OK | | PROCEED TO NEXT SUSPECTED AREA SHOWN IN PROBLEM SYMPTOMS TABLE |
| NG | | REPAIR OR REPLACE HARNESS OR CONNECTOR |
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