Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner
1 - 4 of 4 Posts

2004 chevy trailblazer_ls
18 Posts
Discussion Starter · #1 ·
Hello all,

I am new to this forum but found it because on my 2004 TB my Service Engine Light came on. I took it down to Autozone and they downloaded the codes for me.

First code: P0128 - Coolant temp always low. I've checked my coolant level and all looks well so my next step is going to be to change the thermostat. My truck seemed to run cool because even without the a/c on the air was always pretty cold. Hopefully that will clear this code.

Second code: P0606 - BBECM internal performance error - This one makes me nervous because it states the probably cause is a failed ECM... Could the above code cause this? (crossing fingers, but not hopeful) If not, how much does an average ECM run and would I be able to replace that myself?

Third code: P1680 - BBECM fault condition - Again probably cause ECM not programmed or failed ECM. I am definitely assuming that my ECM has failed and that I would need to replace it. What would be the best place to order one? Should I try my local junk yard?

Last question... where is the ECM located? HAHA, I am going to assume it's in the cab under the dash somewhere.

Well thank you in advance for your assistance.
Jason :hail:

2004 gmc
26,181 Posts
First one definitely thermostat or less likely the sensor. What's your temp gauge been reading while driving steadily? Should be pretty rock solid on 210.

The other ones might just be intermittents. You could try reseating the three connectors to see if it's just oxidation or crud. The computer is on the driver's side of the intake manifold with a big heat sink on the back. If it was really dead the engine wouldn't run.

It's item #1 on this drawing. The thermostat is towards the front of the engine from it, above the arrow labeled "FRT"


2004 chevy trailblazer_ls
18 Posts
Discussion Starter · #3 ·
Thank you for the reply, I will look at all of the connectors on the ECM and make sure they are on solid.

My temps are 5-6 lines below 210deg, which is definitely pretty cool. The temps around here have been around 60-65 deg, but I thought it should run around 210 also since that is the middle location.

What is so ironic... is when I am driving I am always concerned with my temp guage and the vehicle overheating (just a phobia I picked up with my 83 Ranger (found out later the thermostat wasn't even installed)) but never thought my vehicle would run too cool. haha. So I am assuming that it is stuck open since it is running too cool.

I will replace that and see how it goes from there. I will pull my neg bat cable and reset the light and see if it comes back.

I really hope the ECM is just a temp fault!

Thanks for your inputs!

2006 saab 9_7x
84 Posts
On the GM SI (Service Information) website, there is a PI (Preliminary Information) concerning P0606.

#PIP3164B: SES Light Due to a P0606 DTC - Install Updated PCM Calibrations - keywords 4.2 4.2L CEL controls engine lamp LL8 MIL P0606 PCM power reduced - (Sep 8, 2005)

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

On rare occasions, a SES light and a Reduced Engine Power Message may be experienced due a DTC P0606 DTC. This may be due to the software and calibration not being optimum for all driving conditions.

If a Reduced Engine Power Message is not present right now and the P0606 is just a history DTC, reprogram the PCM with the latest calibrations that are available in TIS2000. If the P0606 is resetting, perform the P0606 diagnosis from SI and repair as necessary.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

Here is what it says for P1680:

#PIT3138A: 02-05 Chevrolet, Buick, Oldsmobile and GMC Mid-Sized Utilities Reduced Power Light On and DTC P1680 P1221 and/or P1271 Stored in the PCM - kw fan clutch SES light power MIL 4.2 LL8 - (Nov 1, 2004)The following diagnosis might be helpful if the vehicle exhibits the symptom described in the PI.

Reduced power light on and DTC P1680 P1221 and/or P1271 stored in the PCM

Monitor the 5V reference to the Accelerator Pedal Position ( APP ) sensor, circuit 1274, using Peak Min/Max on a Fluke 87. Refer to Si document 1454678 for the 5V reference schematics. Command the fan clutch control "on" with the Tech 2 at 50%. If when commanding the fan clutch on, the 5V reverence spikes to battery voltage, the concern is the 5V reference shorted to battery voltage intermittently inside cooling fan clutch. Replace the fan clutch to repair this concern.


Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance.

(02 - 05 Chevrolet Trailblazer and Trailblazer EXT) and (02 - 05 GMC Envoy, Envoy XL and Envoy XUV ) and (02 - 05 Buick Rainier) and (02 - 04 Oldsmobile Bravada)

DTC P1680

The throttle actuator control (TAC) system uses two accelerator pedal position (APP) sensors to monitor the pedal position. Two processors are also used to monitor the TAC system data. The Powertrain control module (PCM) performs an intrusive test in order to detect that the APP signals are not shorted together. The PCM accomplishes this by pulling the APP sensor 2 low momentarily and looking for sensor 1 to also be low. The TAC system also performs this test on the throttle position (TP) sensors. This diagnostic monitors the transistor used to pull one pedal and one throttle sensor to ground simultaneously. Additionally, Both processors monitor each other's data to verify that the indicated APP calculation is correct.

If the transistor does not toggle within a calibrated period, or the indicated APP calculation is incorrect , DTC P1680 sets

Conditions for Running the DTC
• The system voltage is more than 5.23 volts.

• The ignition is in Unlock/Accessory or Run position.

• DTCs P0601, P0602, P0604, P0606, P0607 or P1621 are not set.

Conditions for Setting the DTC
• The APP sensor 2 voltage is more than 1.75 volts for more than 0.3 second during the intrusive test.

• or

• The APP sensor calculations in the main processor differ from the motor control processor by more than 0.142 volt.

Action Taken When the DTC Sets
• The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.

• The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.

• The control module commands the TAC system to operate in the Reduced Engine Power mode.

• A message center or an indicator displays Reduced Engine Power.

• Under certain conditions the control module commands the engine OFF.

Conditions for Clearing the MIL/DTC
• The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

• A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

• A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• Clear the MIL and the DTC with a scan tool.
That's the info the techs at the dealership will have to work with when a vehicle showing these codes comes in.
Hopefully this will help.
1 - 4 of 4 Posts