4/24221, 4/24420
Fault Code 4/24221, 4/24420Malfunction indicated
RPM signal/Load signal Tq faulty or absent
Fault symptom
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Test procedure
1 With adapter lead, pan No. 86 11 048, connected, the ignition switch in the Drive position and the engine switched off, enter ISAT command code 281.
The display should now show the pulse length of the load signal in micro-seconds. With the engine switched off, this should be 0 micro-seconds.
2 Start the engine and run it at idling speed. Command code 281 should now result in a load signal of approx. 25 micro-seconds which increases as engine speed increases to approx. 500 microseconds at full throttle.
Alternatively, with the SAT diagnostics lead unplugged from the diagnostics socket, use the pulse measurement function to check whether a change in pulse length and frequency can be measured on pin 27 of the connector as the throttle is opened.
Note: The pulse length and frequency readings displayed by ISAT are not critical. THe important thing is that they change with varying engine speed and load.
3 Repeat the above test procedure, but now with command code 249, to check engine rpm.
4 If incorrect results are obtained in the above test procedure, check the WH and BU/RD leads between pin 27 of the connector and pin 25 of the LH control unit for continuity or shorting to earth.
Also check the OG lead between pin 12 of the connector and pin 29 of the DI/APC control unit for continuity or shorting to earth.
5 Carry out fault tracing on the fuel system.
6 If no faults can be found, clear the fault code and drive the car to see whether it is generated afresh.
If it is, try filling an LH control unit that is known to be OK.
7 Try an ETS control unit which is known to be OK.