From the fault tracing book, Code 131 RPM sensor signal - fault sources- signal lead short circuited to ground - signal lead short circuited to live - signal lead broken - ground lead broken - contact resistance in terminals - RPM sensor defective.

Check RPM sensor - 240 to 400 ohms with engine warm - if ok

Check ground lead - ignition off, sensor disconnected, Connect on ohm meter between RPM sensor connector (to ecm terminal 1, looking at connector with metal spring up it is on the right side)and ground should read approx 0 ohms - if value differs check ecm connector - if ok.

Check signal leads short circuit to live - Ign. on - sensor disconnected - connect volt meter between rpm sensor connector terminal 2 (left side) and ground, should read approx. zero volts. - if value differs check lead between rpm sensors terminal 2 and ecm #47 for short circuit - if ok

Check signal lead resistance - ign. off - sensor disconnected - connect on ohm meter between rpm sensor connector terminal 2 (left side) and ground - should read 10-20 k ohms. - if ok check RPM sensor, if ohm meter reads approx. zero ohms - check lead between sensor connector terminal 2 and ecm #47 for short circuit to ground - If ohmeter reads infinite resistance - check ecm connector

Check RPM sensor - if engine does not start check carrier plate/flywheel for damage and RPM sensor aperture (mounting) If no fault is detected in carrier plate/flywheel test with new RPM sensor.

Hope this helps, I have found this to be the most valuable of the Volvo green books.

I have found that 90% of any faults were corrosion in connectors. You might try not only cleaning the contacts but gently bending them to tighten them up.

DanR 94 964 238,000 miles
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DanR