B1785
Symptom: The message “SERVICE THEFT ALARM” is shown on SID.
Siren. Low Battery
Fault symptoms
The message “SERVICE THEFT ALARM” is shown on SID.
Conditions
Battery voltage should be 11 to 14 volts.
Fault criteria
Low voltage in the siren internal battery.
Diagnostic help
The diagnostic trouble code is generated if a fault is found during two test cycles in succession. A test cycle lasts one second, i.e. it takes two seconds from when the fault occurs until a diagnostic trouble code is generated. If the fault disappears, the trouble code is deleted from the control module memory after the ignition has been turned on 20 times.
Procedure
Replace the siren.
Check wiring harness.
Jiggle the wiring harness at several points and in different directions to reveal intermittent breaks and short-circuits in the leads. Observe the multimeter, test lamp or diagnostic instrument during the test.