Hello, I have a 95 SL which has generally been running fine. Just the other day it started overheating. I determined it was due to the radiator fan not coming on. If I turn on the AC, the condenser fan comes on and the radiator fan comes on for a short time and seems to cycle on for a few seconds from time to time. Temperature gauge is working and reports the over temp condition.
I have checked the following as per the factory service manual.
Radiator fan works with 12v applied.
Fan resistor reading correct.
Coolant temperature sensor reading in various temperatures of hot water correct.
Both high and low speed relays switching with external 12v. and reading good continuity with ohm meter.
Fusable link good.
Fuse block fuse good.
I have not yet checked harness wiring due to low probability of fault (but possible)
What could I be overlooking? If it is the Engine Control Module, is it repairable?
There are multiple temperature sensors for the fan and other operations. Check the manual for the one which operates the relevant fan. I think it is one of the ones at the bottom of the radiator. Also check your coolant fluid levels and that the water is fully circulating around the radiator and engine. If the level is too low or not circulating effectively, the relevant sensor may not get hot enough to switch on the fan. You can check the top and bottom hoses on the radiator. There will only be a relatively small temp difference between them. If there is a big difference, check the thermostat near to the filler opening.
Ok. Thanks. I do not have the sensors on the radiator. Those are on only Gen 1 through 93. After that they are controlled by the one next to the intake manifold. The coolant is topped up. I will check the thermostat. Thanks again.
If the main fan only comes on from time to time with the AC on then my guess would be the fan motor is failing and is tripping a thermal protection inside it.
You could also try swapping the fan relay in the underhood fuse box to see if maybe the relay is weak/failing. You could also “hotwire” the fan via the relay to see if it kicks itself off. Just take the cap off the relay and close the circuit and the fan should run. (key probably needs to be on)
Thanks a lot for all your help and advice. After trying a few of the ideas, I finally went for broke and replaced the capacitors on the ECM. This has solved the issue.