EGR Protective Circuit
Connect Tester (116 589 25 21 00) with "Y" fitting to EGR valve. Run engine to 1200 RPM, then pull off plug on coolant temperature switch and hold against ground. With 10 in. Hg vacuum on EGR valve, cooling fan clutch should come on. If cooling fan is not on, check electrical circuit and repeat test. If circuit is okay, replace ECU.