ENGINE MANAGEMENT SYSTEM - V8: DESCRIPTION AND OPERATION (page 8 of 12)

ENGINE MANAGEMENT SYSTEM - V8

18-2-56 DESCRIPTION AND OPERATION

Function
Input for the rough road signal is measured via pin 34 of connector C0637 of the ECM. The SLABS ECU generates 
a PWM signal that varies in accordance with changing road conditions. The rough road PWM signal operates at a 
frequency of 2.33 Hz 

±

 10%. The significance of changes in the PWM signal are shown in the following table:

The rough road signal can fail in the following ways:

l

Harness or connector damage

l

SLABS failure — wheel speed sensor

A rough road signal failure may be evident from the following:

l

HDC / ABS warning light on

Should a malfunction of the rough road signal occur, the following fault codes may be evident and can be retrieved 
by TestBook:

Hill Descent Control (HDC) signal
The ECM transmits throttle angle, engine torque, engine identification (Td5 or V8), and transmission type (automatic 
or manual) data to the SLABS ECU to support the Hill Descent Control system. The information is transmitted via a 
0 – 12V pulse width modulated (PWM) signal at a frequency of 179.27 Hz. 

Function
The HDC signal output from the ECM is via pin 29 of connector C0636. The ECM generates a PWM signal that varies 
in pulse width in accordance with changing throttle angle or engine torque. The throttle angle data is transmitted on 
pulses 1, 3, 5 and 37. The engine torque data is transmitted on pulses 2,4,6 and 38. The engine and transmission 
information is transmitted on pulse 39. A synchronising pulse is transmitted after every 39th pulse.

The HDC signal can fail in the following ways:

l

Harness or connector damage

A HDC signal failure may be evident from the following:

l

HDC / ABS warning light on

l

HDC inoperative

l

Audible warning

Should a malfunction of the HDC signal occur, the following fault codes may be evident and can be retrieved by 
TestBook:

PWM signal

Indication

<10%

Electrical short circuit to ground

25% 

±

 5 %

Smooth road

50% 

±

 5 %

SLABS error

75% 

±

 5%

Rough road

>90%

Electrical short circuit to battery voltage

P Code

J2012 Description

Land Rover Description

P1590

ABS rough road signal circuit malfunction

Hardware is OK, but SLABS ECU is sending an error 
signal

P1591

ABS rough road signal circuit low

Signal from SLABS ECU short circuit to earth

P1592

ABS rough road signal circuit high

Signal from SLABS ECU short circuit to vehicle battery 
supply

P Code

J2012 Description

Land Rover Description

P1663

Throttle angle/Torque signal circuit malfunction

SLABS HDC link open circuit

P1664

Throttle angle/Torque signal circuit low

SLABS HDC link short circuit to ground

P1665

Throttle angle/Torque signal circuit high

SLABS HDC link short circuit to battery voltage