1994 C280, W202, Engine 104: Not starting & Coolant & Intake air temperature warning

[Arv]

Hello,

1994 C280, W202, Engine 104
I am having an intermittent strange problem for a very long time.

The car cranks very strong but doesn't start till it cools down overnight.

When this happens, I am getting Coolant temp & Intake air temp warning
& OBD2 scanner is showing bogus readings of coolant & intake air temp
out of range even after cooling the car for 6hrs. Tested if the fuel pump runs
when this happens, but seems like the computer shuts down the fuel pump.
I can hear the fuel relays click but fuel pump doesn't start.
ONLY one time, I kept getting serial communication error P0600 but
haven't gotten it again.

Starts just fine when everything is cold at atmospheric temp.

Have changed Crank Position Sensor 2 times, just yesterday,
changed Fuel Filter & Hose, tested the Fuel relays by replacing
with fuel relay. Have just ordered a new MAF.

Also tried changing 2 coolant temperature sensors which are next to
the top of thermostat housing. Haven't tried changing 3rd coolant
temp sensor which is below the thermostat.

Any help is really really appreciated.

Thank you so much,
Arv.

 

[mattkh]

Mileage please,,?
When were the plugs last changed..?

 

[Arv]

Thank you for your reply Matt.

280k miles
It's been over 100k miles since I changed the plugs
& wires. There is no misfiring. The engine runs very
smoothly.

The strangeness of this intermittent problem is it happens
when the hot engine is turned off & sits for a while. If I turn the
engine off & start it right away, it starts immediately.

Shall I try changing them if it fixes the problem?

Thank you,
Arv.

 

[mattkh]

Thanks.
I would just take one plug out and check the gap.
Please take a picture of the plug.

 

[Arv]

Ok, thank you, Will do. Also, could the problem be fuel pump itself also
with it's resistance changing when warm? A possibility.

 

[balge59]

i would test the fuel pump and relay i think. won't start if the pump isn't running. how old is fuel filter?... must get round to doing mine soon...

 

[Arv]

Thank you for your reply balge. Just replaced the fuel filter & hose 2 days
ago & pump is the original one. Also tried installing new fuel relay but
makes no difference.

I was just trying to start the car from cold & getting warning

coolent temp 419
intake air temp 302 warning

& the car is not starting. Cranking very strong.

What's the deal with this warning. Car is completely cold.

Thank you again,
Arv.

 

[Arv]

Hello,

I have 3 Coolant Temperature Sensors near the thermostat housing. Pics
attached.

Blue sensor with 2 wires controls the aux fans.

What do the 1 wire & the other 2 wire round sensor control/activate?

I keep getting Coolant Temp warning of 419 deg on a completely
cold engine in the morning & car doesn't start. Crank/No Start.

At the same time, I also get Intake Air Temp warning of 219deg even
when ambient temp is 80 deg F.

Any feedback is appreciated.

Thank you,
Arv.

 

[mattkh]

Normally the 1-wire one is for the needle of the dash display.

 

[Arv]

Thank you Matt, this is very helpful. I will change the 2-wire round
sensor & see if the temp warning goes away.

Appreciate it a lot,
Arv.

 

[alexanderfoti]

Check the wiring isnt shorted first. This age/year is likely to have deteriorated wiring loom. Especially in hot areas.

 

[Arv]

Thank you Alexander. I think I have fixed the problem which was very simple.

Over time, constant heating & cooling under the hood had made the
all 3 computer harness connections loose. I tapped, pressed down the connections
& tightened the screws to make harness connections on computer firm
& that fixed these strange errors and the car started right away.
I was shocked to find out that the screws were quite loose.
It was causing communication error with the sensors & giving the error.
Now if the car drives without any problem for next 8+ months, then it
will be confirmed that this intermittent problem is permanently fixed.

Thank you all for your help,
Arv.