Time has come to fix CEL previously diagnosed as Fan Fault - Chevy Impala SS Forum
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post #1 of 14 (permalink) Old Yesterday, 09:42 AM Thread Starter
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Time has come to fix CEL previously diagnosed as Fan Fault

I'm pretty sure that's what my local mechanic said when I looked up the flashing code for good old ODB1 diagnostic. He didn't want to go any further than translating the code as he didn't want to chase down electrical gremlins. So I was kind of stuck and took a chance on a local shop 2 blocks over from my office. Talked to the shop owner, and he referred me right next door as he said they have an excellent wiring guy. Walked over and described my problem ( CEL, fans come on right away on engine start, even when ice cold ), and replacing the passenger side fan after the previous owner hit something that dented in the lower radiator/fan support causing the fan to seize.

I did my best to reconnect the harness properly during the R&R of the seized fan, but still have this issue.

I will replace the fan blower resistor as after the critter junk was cleaned out from my HVAC I have only 3 of 4 fan speeds, Low, S2, S2 (same speed as 2nd setting) High.

Really looking forward to having this fixed so I can figure out why the trunk fills with water when it rains... =/

Last edited by ace72ace; Yesterday at 10:37 AM. Reason: typo - trunk not truck
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post #2 of 14 (permalink) Old Yesterday, 10:07 AM
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Walked over and described my problem ( CEL, fans come on right away on engine start, even when ice cold ),/
check your ECT (temp sensor) on front of water pump and the wiring going to it

courtesy of shbox.com

"The PCM gets it's temp readings from a sensor that is in the water pump. It uses two wires. If the reading the PCM receives is inaccurate, the fans may not come on at the correct time. The PCM also uses this temperature for lookup in calculation tables. If there is a problem that causes the reading to be always low (cold), the PCM will add extra fuel. This can cause hard starting when warm and an overly rich condition when running.

The gauge gets it's information from a sensor that is in the driver's side head. It uses one wire. Inaccurate gauge readings can be from this sensor or it's wiring (the wire burned on a header pipe is common). The temp that the PCM sees can be monitored with a scan tool and compared to the gauge reading. They should be close, but don't expect them to be "perfectly" synchronized.

The temperature sensors in the water pump and the cylinder head are not the same. I recommend genuine GM/ACDelco for replacements.

The fans are programmed to come on when the a/c is turned on. A/c Pressure monitoring sensors feed the PCM info and depending on the situation, the PCM may command the fans off for brief periods. If your a/c is broken or operation inhibited because of low refrigerant, the fans will not come on when the a/c is turned on (but will still operate by engine temp). Also, when the car reaches sustained higher speeds, the fans may be commanded off so incoming air can flow through the radiator unimpeded and provide the cooling needed.

Fans will come on when field service mode is initiated and also when the SES lamp comes on. The PCM does this when certain (most) DTCs are detected to protect the engine from a situation where it may overheat."

use a DVM to measure the resistance of the temp sensor on the water pump per this chart

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post #3 of 14 (permalink) Old Yesterday, 10:38 AM Thread Starter
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Thanks! Always want to take a stab at the DIY method for cost savings and learning.

On second thought, I just read through the information provided and decided that beyond checking for a disconnected/burnt wire on a visual inspection I'd rather pay a pro.

Last edited by ace72ace; Yesterday at 10:44 AM.
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post #4 of 14 (permalink) Old Yesterday, 10:49 AM
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If you have a obd reader that can display live data, you can see what it shows for the ECT temperature. If it's looking valid, you probably don't need the DVMM to buz anything out.


For your trunk water, check the seams at the top of the quarter panels where they meet the roof. It's about 6 inches long. The painted caulking there dries up, cracks and lets water in.
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post #5 of 14 (permalink) Old Yesterday, 10:52 AM Thread Starter
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Thanks, no reader, and this is ODB1, just flashing indicator. I will have a look at the trunk as well.
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post #6 of 14 (permalink) Old Yesterday, 11:01 AM
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OBD 1 will give you live data too in case you didn't know. And it would show IIRC like a huge negative temp if there is a break in the circuit or bad sensor.
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post #7 of 14 (permalink) Old Yesterday, 11:33 AM
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Thanks! Always want to take a stab at the DIY method for cost savings and learning.

On second thought, I just read through the information provided and decided that beyond checking for a disconnected/burnt wire on a visual inspection I'd rather pay a pro.
It takes 5 seconds to check sensor with a DVM for ohms....but if you want to pay someone to do that fine.Ö.but that person would need to know wtf the ohms should be....assuming he even knows the WP ECI sensor can cause both fans to come on at cold start

This may not be your problem but for less effort than it takes to unscrew a gas cap to check....
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post #8 of 14 (permalink) Old Today, 09:49 AM Thread Starter
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Yep, I get it, but I'm at the point where I just need it fixed - no matter how simple it is to check X, Y, Z. I was assured their 'wiring guy' is the best and knows his bleep. So we'll see how it goes.

I couldn't see any evidence of bad caulk on the rear quarters, just a little crack in it in the top of the 2nd pic. Will look at this area more closely and check for moisture underneath that area.

Also changed the oil and put new rubber on my 'other' baby.






Last edited by ace72ace; Today at 10:17 AM. Reason: typo
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post #9 of 14 (permalink) Old Today, 10:23 AM
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I'm pretty sure that's what my local mechanic said when I looked up the flashing code for good old ODB1 diagnostic. He didn't want to go any further than translating the code as he didn't want to chase down electrical gremlins. So I was kind of stuck and took a chance on a local shop 2 blocks over from my office. Talked to the shop owner, and he referred me right next door as he said they have an excellent wiring guy. Walked over and described my problem ( CEL, fans come on right away on engine start, even when ice cold ), and replacing the passenger side fan after the previous owner hit something that dented in the lower radiator/fan support causing the fan to seize.

I did my best to reconnect the harness properly during the R&R of the seized fan, but still have this issue.

I will replace the fan blower resistor as after the critter junk was cleaned out from my HVAC I have only 3 of 4 fan speeds, Low, S2, S2 (same speed as 2nd setting) High.

Really looking forward to having this fixed so I can figure out why the trunk fills with water when it rains... =/
You are aware that the HVAC fan has nothing to do with the engine fans, don't you?

Just wondering why blower resistor, 3 of 4 speeds, etc., was inserted in your OP.

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Last edited by grandpas wagon; Today at 10:27 AM.
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post #10 of 14 (permalink) Old Today, 10:29 AM Thread Starter
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Yes, I'm aware of that. Was just commenting on the status of my HVAC regarding an old post from last year.
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