pr0xZen

Previous CTS was off by a mile on G62 (Engine signal), and showing 30.0'C on the cluster (G2) with VCDS. Got a new CTS (genuine), bench (kettle) tested it, both sides within spec all the way. After change, G62 (Engine signal) is pretty much dead on, all good. But the checking the cluster groups, it still reads 30.0'C. Even when disconnecting the CTS connector, it still reads 30.0'C.

Cluster (Analog clock, VDO) output test seems good, sweeps and stops vertical (90'C).

Any takers?

SloopJohnB@mac.com

Bentley/eBahn would suggest the issue is with the engine ECM.

Audi > C5 > 1998-2005
2.8 Liter V6 5V Generic Scan Tool, Engine Code(s): AHA, ATQ
24 - Components, Checking.Engine Coolant Temperature Sensor, Checking
Engine Coolant Temperature Sensor, Engine Code ATQ

CAUTION!
Cooling system is under pressure.
Danger of scalding when opening!

Note:

Use only gold-plated terminals when servicing terminals in the electrical harness connector of Engine Coolant Temperature (ECT) Sensor G62 .

Special tools, testers and auxiliary items required

Multimeter .

jumper wire .

Wiring diagram.

Test requirements

The Engine Control Module (ECM) J220 fuses OK.

Battery voltage at least 12.5 volts.

All electrical consumers such as, lights and rear window defroster, switched off.

Vehicles with automatic transmission, shift selector lever into position "P" or "N" .

A/C switched off.

Ground (GND) connections between engine/transmission/chassis OK.

Ignition switched off.

Engine cold.

Test procedure

Perform a preliminary check to verify the customers complaint. Refer to Preliminary Check

Start diagnosis

Connect the scan tool.

Switch the ignition on.

Using the scan tool, check the coolant temperature:

Diagnostic text Specified value
Coolant temperature Approx. coolant temperature
If the specified value is not obtained:

Continue test according to the following table:

Indicated Cause Test
approx. -40.0 ° C Open circuit or short circuit to (B+)
approx. 140.0 ° C Short circuit to Ground (GND)
If the specified value was obtained:

Start the engine and let it run at idle.

The temperature value must increase uniformly in increments of 1.0 degree C.

If the engine shows problems in certain temperature ranges and if the temperature does not climb uniformly, the temperature signal is intermittent.

Replace the the Engine Coolant Temperature (ECT) Sensor G62 .

Checking internal resistance

Disconnect the Engine Coolant Temperature (ECT) Sensor G62 electrical harness connector.

Using a multimeter , check the Engine Coolant Temperature (ECT) Sensor G62 terminals C to D for resistance.

Use the chart below for the specified values:

Area A: Resistance values 0 to 50 degree C.

Area B: Resistance values 50 to 100 degree C.

Specified values:

Range A, 30 degree C equals a resistance of 1.5 to 2.0 kΩ

Range B, 80 degree C equals a resistance of 275 to 375Ω

If any of the specified values was not obtained:

Replace the Engine Coolant Temperature (ECT) Sensor G62 .

. Testing if display is approx. - 40.0 degree C:

Disconnect the Engine Coolant Temperature (ECT) Sensor G62 electrical harness connector .

Using a jumper wire , connect the Engine Coolant Temperature (ECT) Sensor G62 electrical harness connector terminals 1 to 2.

Check the value indicated on the scan tool display.

If the value jumps to approx. 140.0 degree C

End diagnosis and switch the ignition off.

Replace the Engine Coolant Temperature (ECT) Sensor G62 .

If indication remains at approx. -40.0 degree C:

. Testing if display approx. 140.0 degree C:

Disconnect the Engine Coolant Temperature (ECT) Sensor G62 electrical harness connector.

If indication jumps to approx. -40.0 degree C:

End diagnosis and switch ignition off.

Replace the Engine Coolant Temperature (ECT) Sensor G62 .

If indication remains at approx. 140.0 degree C:

Checking wiring

If the manufacturers test box is being used. Perform the following step.

Install the Test Box 105 Pin VAG1598/31 (Engine Code ATQ ) Test Box 80 Pin VAG1598/22 (Engine Code AHA). Refer to Fuel Injection and Ignition - Repair Group 01 .

If the manufacturers test box is not being used. Perform the following step.

Remove the Engine Control Module (ECM) J220 . Refer to Engine Control Module, Replacing .

Using a Multimeter , check the Engine Coolant Temperature (ECT) Sensor G62 electrical harness connector terminals to the Engine Control Module (ECM) J220 electrical harness connector T121 terminals for resistance.

Engine Coolant Temperature (ECT) Sensor G62 electrical harness connector terminals Engine Control Module (ECM) J220 electrical connector 121 terminals or test box socket
3 108
4 93
Specified value: 1.5 Ω Max.

If the specification was not obtained:

Check the wiring for a short circuit to each other, Battery (+), and Ground (GND).

Check the electrical harness connector for damage, corrosion, loose or broken terminals.

If necessary, repair the faulty wiring connection.

If no malfunction is detected in the wiring:

Erase the DTC memory. Refer to Diagnostic Mode 04 - Erase DTC Memory

Perform a road test to verify repair.

If the DTC does not return:

Repair complete, Generate readiness code. Refer to Readiness Code .

End diagnosis.

If the DTC does return and no malfunction is detected in the wiring and the voltage supply was OK:

Replace the Engine Control Module (ECM) J220 . Refer to Engine Control Module, Replacing .

Assembly is performed in the reverse of the removal.

Final procedures

After repair work, the following work steps must be performed in the following sequence:

Check the DTC memory. Refer to .
If necessary, erase the DTC memory. Refer to .
If the DTC memory was erased, generate readiness code. Refer to .

End of diagnosis.

Engine Coolant Temperature Sensor, Engine Code AHA

CAUTION!
Cooling system is under pressure.
Danger of scalding when opening!

Note:

Use only gold-plated terminals when servicing terminals in the electrical harness connector of Engine Coolant Temperature (ECT) Sensor G62 .

Special tools, testers and auxiliary items required

Multimeter .

jumper wire .

Wiring diagram.

Test requirements

The Engine Control Module (ECM) J220 fuses OK.

Battery voltage at least 12.5 volts.

All electrical consumers such as, lights and rear window defroster, switched off.

Vehicles with automatic transmission, shift selector lever into position "P" or "N" .

A/C switched off.

Ground (GND) connections between engine/transmission/chassis OK.

Ignition switched off.

Engine cold.

Test procedure

Perform a preliminary check to verify the customers complaint. Refer to Preliminary Check

Start diagnosis

Connect the scan tool.

Switch the ignition on.

Using the scan tool, check the coolant temperature:

Diagnostic text Specified value
Coolant temperature Approx. coolant temperature
If the specified value is not obtained:

Continue test according to the following table:

Indicated Cause Test
approx. -40.0 ° C Open circuit or short circuit to (B+)
approx. 140.0 ° C Short circuit to Ground (GND)
If the specified value was obtained:

Start the engine and let it run at idle.

The temperature value must increase uniformly in increments of 1.0 degree C.

If the engine shows problems in certain temperature ranges and if the temperature does not climb uniformly, the temperature signal is intermittent.

Replace the the Engine Coolant Temperature (ECT) Sensor G62 .

Checking internal resistance

Disconnect the Engine Coolant Temperature (ECT) Sensor G62 electrical harness connector.

Using a multimeter , check the Engine Coolant Temperature (ECT) Sensor G62 terminals 1 to 3 for resistance.

Use the chart below for the specified values:

Area A: Resistance values 0 to 50 degree C.

Area B: Resistance values 50 to 100 degree C.

Specified values:

Range A, 30 degree C equals a resistance of 1.5 to 2.0 kΩ

Range B, 80 degree C equals a resistance of 275 to 375Ω

If any of the specified values was not obtained:

Replace the Engine Coolant Temperature (ECT) Sensor G62 .

. Testing if display is approx. - 40.0 degree C:

Disconnect the Engine Coolant Temperature (ECT) Sensor G62 electrical harness connector.

Using a jumper wire , connect the Engine Coolant Temperature (ECT) Sensor G62 electrical harness connector terminals 1 to 3.

Check the value indicated on the scan tool display.

If the value jumps to approx. 140.0 degree C

End diagnosis and switch the ignition off.

Replace the Engine Coolant Temperature (ECT) Sensor G62 .

If indication remains at approx. -40.0 degree C:

. Testing if display approx. 140.0 degree C:

Disconnect the Engine Coolant Temperature (ECT) Sensor G62 electrical harness connector.

If indication jumps to approx. -40.0 degree C:

End diagnosis and switch ignition off.

Replace the Engine Coolant Temperature (ECT) Sensor G62 .

If indication remains at approx. 140.0 degree C:

Checking wiring

If the manufacturers test box is being used. Perform the following step.

Install the Test Box 105 Pin VAG1598/31 (Engine Code ATQ ) Test Box 80 Pin VAG1598/22 (Engine Code AHA). Refer to Fuel Injection and Ignition - Repair Group 01 .

If the manufacturers test box is not being used. Perform the following step.

Remove the Engine Control Module (ECM) J220 . Refer to Engine Control Module, Replacing .

Using a Multimeter , check the Engine Coolant Temperature (ECT) Sensor G62 electrical harness connector terminals to the Engine Control Module (ECM) J220 electrical harness connector T80 terminals for resistance.

Engine Coolant Temperature (ECT) Sensor G62 electrical harness connector terminals Engine Control Module (ECM) J220 electrical connector 80 terminals or test box socket
1 53
3 67
Specified value: 1.5 Ω Max.

If the specification was not obtained:

Check the wiring for a short circuit to each other, Battery (+), and Ground (GND).

Check the electrical harness connector for damage, corrosion, loose or broken terminals.

If necessary, repair the faulty wiring connection.

If no malfunction is detected in the wiring:

Erase the DTC memory. Refer to Diagnostic Mode 04 - Erase DTC Memory

Perform a road test to verify repair.

If the DTC does not return:

Repair complete, Generate readiness code. Refer to Readiness Code .

End diagnosis.

If the DTC does return and no malfunction is detected in the wiring and the voltage supply was OK:

Replace the Engine Control Module (ECM) J220 . Refer to Engine Control Module, Replacing .

Assembly is performed in the reverse of the removal.

Final procedures

After repair work, the following work steps must be performed in the following sequence:

Check the DTC memory. Refer to .
If necessary, erase the DTC memory. Refer to .
If the DTC memory was erased, generate readiness code. Refer to .

End of diagnosis.


Copyright © 2008 Audi of America, Inc. and Bentley Publishers. All rights reserved. Last processed:

pr0xZen

As recently covered here - the Bentley instructions only covers the G62/ECM side - they do not touch on troubleshooting or testing, on the cluster/instrument panel (G2) side. These are completely separate circuits, even internally in the sensor.


Got a reply for Aragorn over at AudiSRS - Apparently, 30.0'C is the lowest temperature the cluster will read. As long as it performs as expected once coolant temp goes above 30.0'C, its fine.

Kind of makes sense - cluster reading is only for the gauge, and reading values much above or below the gauges' display capacity, isn't that useful, and saves on scarce EEPROM space. The sensors resistance increases, as the temperature decreases. If the cluster readings "bottom out" at 30.0'C, any resistance larger than specified for this temperature will still "read" 30.0'C. Pulling the plug completely means unlimited resistance, the cluster programming doesn't incorporate a "cricuit break" code. Only the ECM side does.

Case solved!

Note: Of course, this means that if you still see 30.0'C at the cluster, knowing that the coolant temperature is clearly above that - and Cluster Output test is OK... that doesn't neccessarily mean a faulty CTS. It could be a broken circuit (wire break or blown fuse, not sure if that circuit is fused).

jcman

Then you be able use a resistor with a value that corresponds to 90c and jumper 2-4 instead of flat out shorting it (no harm to the cluster), if nothing registers then there is a break in the ground to the cluster or the input to the cluster, try a 200ohm resistor or any value lower.

pr0xZen

This is not a bad idea at all! Looking at the G62 side, my bench-results and the slight deviation on my G2 side - comparing it to VCDS data from engine and cluster today... If you want the cluster to show ~90'C, I think you're looking at about 110 ohm.

I'm probably going to have to change some seals around the throttle body to get at the last vacuum leaks- I'll try to remember testing a few resistors and see if I can't fork up some more precise numbers. Could sum up a nice ammendment to the Bentley PDF you posted.

-

Now if I remember correctly from my recent dig through several forums, I believe the cluster guage does not really show precise measurements - but will stay around the 90'C (vertical) mark, even if the actual temp is between ~80'C and 100'C. The cluster displays by a curve, amplituded around 90. Now if checking measuring blocks at the cluster with VCDS / Vag-com, you'll get a "precise number". AFAIK, it is actually possible to recode the cluster to show a much more precise temp by making that curve linear, but it involves reading and flashing, calculating new values and custom hex tweaking of the cluster EEPROM.

jcman

I believe that the not so precise measurement is based on Hysteresis (IE: between the point of A&B only), this would allow the gauge to not swing back and forth and to buffer the dead-band area. I use these settings on VFD fan controls with a thermistor mounted on a outdoor condenser refrigeration hot discharge line to ramp-up or down speed to keep a pressure in an operating envelope and this also applies to direct fired gas modulating valves that heat outdoor air and maintain a set supply temp entering an area without a "hunting flame"......I think you get the picture.

Or.... It just reads a certain narrow ohm range within the clusters processor before it sends a signal to the gauge.

pr0xZen

I think I understand what you mean. As in regards to the guy who explained how to do the "mod", he explained it (how it works, program wise in the cluster) more precise than I ever could: here

Had a couple of shorter runs today, and watched the fuel trim logs when I got home. Still doesn't seem quite right, wobbles alot near/around the 10% mark. Can't really wrap my head around it though, I'm very new to all this. Can't really see "the thread", whats causing what. But when playing back a log from before changing the CTS (again), not to mention patching up most of those huge vacuum leaks - its clear that its much better than it was before. Dropped from avg +20-25% STFT on idle, to ~5%.

Funny thing, the whole time I was diddling around with the "old new" CTS (and vac leaks), it would never establish long term fuel trim. Today, it took 5 minutes after clearing codes and TBA.

jcman

Fuel trims are also reliant on pre O2 sensors and I believe MAF too, how old are your O2 sensors? When they are old they are slow to respond.

So far it sounds like your getting things in order though.

jcman

Hey pr0xZen,

Very of topic but have or do you know about Jamo speakers?
I have a SW-500 isobaric twin 10" passive sub from 92 and just re-foamed the drivers, the thing is a beast!
Not many folks over here have this model.

pr0xZen

As I bought the car from an "there's wheels, and I think there's xenon" (no there isn't.....yet) - kind of guy, I've been heavily dependant on paperwork for history. Luckily all (4) previous owners have seemingly been heavily dependant on Audi dealership for pretty much any work, so the paper trail is decent. Either one or both pre-cat O2-sensors (and MAF) were changed, but that was 13 years/200kkm ago.

(Also had an idler pulley break after timing belt job at the dealership - according to paperwork, both complete heads replaced with Audi factory replacements @ 100kkm ago).

The old-age tardiness might explain what I've been seeing on the log playbacks from yesterday. When holding steady load and RPM, or braking down and idling (eg, an intersection) - the STFT graphs will start off pretty zig-zag hairy, and slowly reduce their +/- play towards fairly reasonable numbers. Not sure if thats it, but in my feeble mind.... Idle isn't what I'm worried about though, the zig-zagging has a lot more muchiness to it at other rpm's.

Well, I started taking this O-T with my fuel trim rants, I don't mind I haven't really owned Jamo speakers myself, but some friends have through the years. The S-W500 is quite a grown-up tandem-puppy isn't it? I've read some things about people finding it a bit boomy, but crossover and/or port tweaks will remedy that - if its really an issue. Sound is highly subjective. Over here they show up used for anything from ~$80-$200, depending on current state, handling, modification etc.

Personally I have a frankenstein system, patched together by what I find as a good used deal there and then; 10" small, 100w C-W active sub, Dali Ikon Vokal 2 MK2 center, Dali 606 fronts and Earthquake Platine Noiree (PN1411) rears on DIY adjustable stands (couch against the rear wall). All run by an old NAD T754, "with slight pulling help" from an even older Rotel RB-985 THX power amp.

Honestly its really too big and capable for 25 square meter living room, hasn't gotten "aired out" since it all came together i think. But I love it

Actually looking to find a descrete way to get some slight ompf in the Audi (avant), have seen custom ~15 liter 10" boxes made for the rear side cubby holes. Looks interesting. Car does not have the Bose system, so should be spare room on the other side for an amp.