Help me diagnose: 2000 Accord with idle jump, check engine on

The following symptoms, which may or may not all be related, are all
happening with my 2000 Accord EX Coupe:

* Check Engine light is on, code P1486 (Thermostat Range/Performance
Problem)
* AC stopped getting cold
* Idle periodically fluctuates back and forth from just under 1000 RPM
to about 2000. Doesn't do this for very long usually, and happens
most often at startup.

The temp gauge reads normal -- right in the middle at the hottest.
The RPMs do drop when A/C button is turned on.

Anyone look at this and say, "I know! I've seen this!" or at least
have any ideas what's going on? I'd love to not spend lots of
unnecessary money replacing one thing after another if there's a
likely culprit (if these are even all related).

Thanks!

 

absolutely not. no. d.a.g.s of this group. coolant level.

 

absolutely not. no. d.a.g.s of this group. coolant level.

 

Coolant sensor?

 

Coolant sensor?

 

you can measure resistance of a coolant temp sensor(CTS) to see if it's OK.
it's just a thermistor. I had one that was open.
(there's a separate sender for the dash temp gauge.)

Also,coolant level is important.(not what's in the expansion tank,but in
the engine itself;some Hondas have a air-bleed port to get rid of excess
air in the block.

 

See your local Honda dealer regarding TSB 01-022. You may need a new PCM.

Also, how old is the thermostat?

 

See your local Honda dealer regarding TSB 01-022. You may need a new PCM.

Also, how old is the thermostat?

 

not quite that simple though apparently. i've messed about with a few
recently, and while they may test ok with the resistance function of a
multimeter, they're still sending the wrong [too cold] signal to the
ecu. replacing with a new one shows the difference in performance -
10-15% better gas consumption.

with the 2000 accord, diagnostics are easier - you can plug in an obd
reader and see what temperature it thinks it's seeing.

indeed.

 

Then they would NOT be "testing OK" ...to specs.(properly tested)
A thermistor has to read a specific resistance at a specific temp.(within
tolerances)
Or else your ohmmeter is inaccurate.

 

well, i'm reporting my test results. and they are consistent across a
number of sensors and two same-type cars.

what ohm meters /don't/ do is test at higher currents like those in
service. since the thermistor is a [non-ohmic] semiconductor [negative
temperature coefficient], i don't see a reason why it can't degrade
after thousands of hours at higher temperatures, lose carriers, and thus
sustain a lower current density than that needed to give an accurate
result to the ecu, but still maintain the minimal current when connected
an ohm meter.

what i should do next is put the thermistor in a wheatstone bridge to
test at higher currents and see if that shows what is observed when the
sensor is in the car.

 

they don't run a "high current" thru a thermistor to measure temp.
it need only be a few milliamps.it's part of a voltage divider.

what sort of currents do you believe are used for thermistors in an auto?

 

i don't know - i've never measured. if you know, what is the difference
between that and a dvm?

 

between WHAT and a DVM?
are you asking about what currents a DVM uses to measure resistance?
it depends on what range,but for say the 2Kohm(FS) range,it would be 1 ma.
on a 2V full scale meter.

not enough difference to affect a thermistor measurement.

 

NHTSA Item Number: 637949
Service Bulletin #: 402
Replacement #:
Vehicle/Equipment Make: HONDA
Vehicle/Eqipment Model: ACCORD
Model Year:
Mfg Component Code: 116200 ELECTRICAL SYSTEM:IGNITION:MODULE
Date of Bulletin: 2002-04-16
Date Added: 2002-12-09
Summary: SUBJECT REGARDING DIAGNOSTIC TROUBLE CODE P1486.

http://wiki.answers.com/Q/What_is_the_code_p1486_for_honda_accord_2000

This can be a tricky code to diagnose if you don't have the right
tools and equipment.

DTC P0128 and/or P1486 can set occasionally just because the hood is
opened. If your DTC during conditions other than that, read the
following:

Check the engine coolant level. Is the engine coolant level low?
YES - Refill the engine coolant. If necessary, check the cooling
system.
NO - Go to step 2.

Turn the ignition switch ON, and make sure the A/C is off.
Check the radiator fan. Does the radiator fan keep running?
YES - Check the radiator fan circuit with A/C model or without A/C
model, radiator fan switch circuit, and the radiator fan switch. If
the circuits and the switch are OK, substitute a known-good ECM/PCM
and recheck. If the symptom/indication goes away, replace the original
ECM/PCM.
NO - Test the thermostat.

 

NHTSA Item Number: 637949
Service Bulletin #: 402
Replacement #:
Vehicle/Equipment Make: HONDA
Vehicle/Eqipment Model: ACCORD
Model Year:
Mfg Component Code: 116200 ELECTRICAL SYSTEM:IGNITION:MODULE
Date of Bulletin: 2002-04-16
Date Added: 2002-12-09
Summary: SUBJECT REGARDING DIAGNOSTIC TROUBLE CODE P1486.

http://wiki.answers.com/Q/What_is_the_code_p1486_for_honda_accord_2000

This can be a tricky code to diagnose if you don't have the right
tools and equipment.

DTC P0128 and/or P1486 can set occasionally just because the hood is
opened. If your DTC during conditions other than that, read the
following:

Check the engine coolant level. Is the engine coolant level low?
YES - Refill the engine coolant. If necessary, check the cooling
system.
NO - Go to step 2.

Turn the ignition switch ON, and make sure the A/C is off.
Check the radiator fan. Does the radiator fan keep running?
YES - Check the radiator fan circuit with A/C model or without A/C
model, radiator fan switch circuit, and the radiator fan switch. If
the circuits and the switch are OK, substitute a known-good ECM/PCM
and recheck. If the symptom/indication goes away, replace the original
ECM/PCM.
NO - Test the thermostat.

 

the ecu - what else would the tw sensor be connected to?

1mA delta can make a huge difference with a semiconductor.

 

not with a thermistor.