code P0128

[wardy 0]

Hi 

My car is my 2002.

 

I have a CEL alarm with the code P0128, "coolant temperature below thermostat regulating temperature"

 

I am not able to remove this alarm with OBD II 

 

There is a reference to this alarm in 2006 but I can not see an answer in this posting

 

The engine coolant temp seems good at 88 / 90 degs.

 

Is there a sensor which reads this temp within a time frame ?

 

What puts this alarm on ?

 

How do I remove it ?

 

Hope these questions make sense.

 

  Thanks,  Chris

 

 

[Günter 27 1 Vehicles]

there is no such code in the lotus-manual .by the way (you can have P0116 up to P0118) for the coolant-temperature sender. Normally the backfeed of the static voltage reference from the ECM pins should be there between 0.562volt to up to 4.31volt   anything outside this gives 'fault criteria' notes

 

-so what is the 'engine-cooling temperature' parameter showing on the live-parameter map there on your OBD tool ?

(do you use a simple memory coder-reader, or a stand alone/PC based OBD live parameter/data logger   ..so a device that can show 'realtime-maps' on a screen and graphs too)

 

..if your cooland temperature sender for the ecu sees wrong signals, and sends this information to the ECM the engine management computer calculates 'plausibility causes' (warm up time requirements/ air temperature correspondance and such things) ..and notes that there is fault/false signal.

 

both temperature senders for the water temperature are on top of the engine block, front end of it ..next to the thermostat takeoff & crankase breather port and knock sensor -you can see them if you sit with your knees in the rear boot, and look there with your head on the engine frontside under the plenum

.. so if you are not handy enough undo the plenum to inspect measure the sender electric function. 

 

see item-nb *14 & 15 there

..the smaller one (with one pin, there the 'electric ground' is on the engine-block) this is for your instrument cluster 

..and the other one is ECM reference (two pins)

 

you should use the workshopbook, this gives information on the engine-management as well as on the position/layout of all those sensors & functions

[wardy 0]

Hi Gunter

Once again thank you for your quick reply to my questions.

 

As you suggested I checked the temp sender for possible bad connections and high resistance.

 

When unplugged all looked good, at approx 10degs the resistance was about 4500 ohms.

 

I cleaned up the plug and sender socket and applied a small amount of contact cleaner.

 

I connected my OBD II sensor ( this is pc based ) and monitored the temp in real time.

 

The engine was started from "cold" fault code p0128 still ON and unable to clear.

 

After 320 seconds running ( see info in workshop book ) temp indicating 60 degs.

 

After 12 mins running (tick over speed, car in garage) temp at 82 degs.

 

Temp then went up slowly until the fans switched in at 100 degs 

 

At 95 degs fans switched off.

 

I then tried to cancel / remove the P0128 alarm -- no luck -- I tried three more times and at the last a try the alarm was removed and the CEL was off

 

The engine was switched off and re started several times -- still no alarm.

 

On the pc display the alarm is still logged but no CEL.

 

I will monitor and inform you if the alarm returns.

 

Thanks very much for your help

 

  Chris Ward

[Günter 27 1 Vehicles]

curious Fault-code, as it does not exist in the workshoplist  ..at least not related to coolant temperature sender

 

Not sure on the type of sender, so instead of 'resistance' unplugged I would measure the voltage there in the wiring line and compare that with the manual reference (see notes above)

[wardy 0]

Hi Gunter

Sorry to say but after just 40 miles driving P0128 returned and again will not cancel.

 

Unplugged the temp sensor as I did before but this time the alarm will not cancel no matter how many times I try.

 

As you say code P0128 is not listed in the lotus manuals that I have.

 

Below is part of a post from year 2006.

 

What do you make of the special ECU learning procedure ?

 

P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

 

 

"I don't know the meaning of this code, but I did have a very similar experience with my 02 V8. see my post.
To cut a long story short, the ECU needed to re-learn the output of some sensors. Until I performed a very special ECU learning procedure, I couldn't clear the error code at all with my OBD software.
Ask your Lotus dealer to check for updates from Lotus - that's where my Lotus dealer found the solution."

  Chris

 

[Günter 27 1 Vehicles]

there is a type 'constant drive' cycle noted in here in the forum (V8 section)  ..think he refers to this

 

..need to find it for you, or you use the search function for your own..

Edited April 12, 2013 by Günter

[wardy 0]

Hi Gunter

 

Please forgive me but I am not very good when trying to search for things on the forum.

 

When I tried to search  'constant drive'. I just got your posting.

 

Do you think that the reference to engine temp and time is not connected to the alarm and that it is caused by something else.

 

It is annoying that I can not remove this alarm.

 

Thanks for your help

 

  Chris

 

[WEllison 9]

There is something else causing the bogus P0128 error code to be set. The OBD2 scanner indicates that the ECU is "seeing" normal temperature swings. I've seen and heard of other "non listed" strange error codes being set in the ECU. There are drive cycles that can be followed to set the conditions to allow the rediness tests to run, but that's not what you need here. There is some strange set of conditions which are causing the ECU to set this non-standard (for an Esprit V8) error code. There was a posting in 2008, on another forum, about an Esprit V8 that had an P0128 error code along with a bunch of other codes, but no reported solution. I hate generalized fixes, but try cleaning all the engine gound connections on the bell housing???

[oneshot 85 1 Vehicles]

Just a thought - do you have the standard Lotus ECM? P0128 "coolant temp below temp" is a generic OBD2 error code that is apparently not used by Lotus although some websites seem to indicate it is used.

 

This site has someone who had the error - turned out to be a faulty thermostat.

[wardy 0]

Hi Gunter, Wayne and Dave

 More about the fault code P0128 that lotus do not use.

Thanks for your input with my problem. Dave suggested looking at " Lotus Talk .com ". On this site There is a link which gives more info.The code is used by many manufactures to indicate possible problem with the thermostat.

The ECU takes info from several things to determine this. One of the inputs is the IAT sensor.

At this time I had not checked this system. From the Lotus workshop book I got the resistance values for the sensor. When I checked this the results did not seem correct. I removed the sensor for closer inspection. The sensor terminates in two small "male" pins onto which the plug connects. Viewed through a magnifying glass I could see debris between the pins. The pin connection area and the plug were cleaned. After refitting the sensor the engine was run and the IAT temp monitored via OBDII. it looked good.

The CEL light was removed when I tried to cancel the alarm but the fault code remained logged.

Since this I have driven 150 miles and no return of the CEL.

I will get back to you if the CEL returns ( fingers crossed )

Do you think the logged alarm will clear after a number of engine start conditions

 

Once again thanks for your help.

     Chris

 

[Günter 27 1 Vehicles]

'normally' if you bride/shortcut the IAT sensor connector it shows a own fault code, pointing out that the IAT is 'out of range' or more or less 'to low' compared to logic causes .. and the fault-code description says that a 'pre set specified value' (40°C) is used as substitute instead of the wrong IAT signal, so the ECM refers to other sensors (water temperature) o this fixed substitute value as orientation in this case

 

..still not sure why there should be a fault code that is actualy not used by Lotus  ??

 

..