SES light; throws code 43... '87 Silverado w/350

[RMC_SS_LDO]

I am getting a recurring SES light.  All I have available to identify it is to jumper the connector and decode the flashes. 

If I am decoding this correctly, it is throwing code 43 indicating a problem with the Electronic Spark Control (ESC) module or the knock sensor.

Just wondering if this code is common?  I intend to try replacing the knock sensor then the ESC module, but I am just wondering if there is a root cause that could be causing the error or is it actually the sensor/ESC module?

Thanks in advance!

/r

Allen

[Captkaos]

43 generally means a bad knock sensor.

[RMC_SS_LDO]

Thanks for the tip!

I will be doing a thermostat swap and a flush and fill this weekend.  While it's drained, I'll crawl under and try to swap the knock sensor out.

[Josh454]

When you replaced the knock sensor becareful not to over torque it.

[VileZambonie]

This ought to help





CODE 43 - ELECTRONIC SPARK CONTROL (ESC) CIRCUIT



 Circuit Description :

Electronic spark control is accomplished with a module that sends a voltage signal to the ECM. As the knock sensor detects engine knock, the voltage from the ESC module to the ECM drops, and this signals the ECM to retard timing. The ECM will retard the timing when knock is detected and RPM is above about 900 RPM.

Code 43 means the ECM has been low voltage at CKT 485 terminal "B7" for longer than 5 seconds with the engine running or the system has failed the functional check.

This system performs a functional check once per start-up to check the ESC system. To perform this test, the ECM will advance the spark when coolant is above 95~C and at a high load condition (near W.O.T.). The ECM then checks the signal at "B7" to see if a knock is detected. The functional check is performed once per start-up and if knock is detected when coolant is below 95~C (194~F), the test has passed and the functional check will not be run. If the functional check fails, the "Service Engine Soon" light will remain "ON" until ignition is turned "OFF" or until a knock signal is detected.



 Test Description : Numbers below refer to circled numbers on the diagnostic chart.

If the conditions for a Code 43 are present, the "Scan" will always display "YES." There should not be a knock at idle unless an internal engine problem, or a system problem exists.
This test will determine if the system is functioning at this time. Usually a knock signal can be generated by tapping on the right exhaust manifold. If no knock signal is generated, try tapping on block close to the area of the sensor.
Because Code 43 sets when the signal voltage on CKT 485 remains low, this test should cause the signal on CKT 485 to go high, The 12 volts signal should be seen by the ECM as "no knock" if the ECM and wiring are OK.
This test will determine if the knock signal is being detected on CKT 496 or if the ESC module is at fault.
If CKT 496 is routed to close to secondary ignition wires, the ESC module may see the interference as a knock signal.
This checks the ground circuit to the module. An open ground will cause the voltage on CKT 485 to be about 12 volts which would cause the Code 43 functional test to fail.
Connecting CKT 496 with a test light to 12 volts should generate a knock signal. This will determine if the ESC module is operating correctly.
 Diagnostic Aids :

Code 43 can be caused by a faulty connection at the knock sensor at the ESC module or at the ECM, Also check CKT 485 for possible open or short to ground.

[VileZambonie]

Direct link for full size

Click

here

[RMC_SS_LDO]

Thanks so much!

Unfortunately I don't have access to a scanner to properly troubleshoot the problem, but one part of the description seems particularly applicable.

The SES light comes on during normal driving, steering me toward a failure of on the routine functional check:

This system performs a functional check once per start-up to check the ESC system. To perform this test, the ECM will advance the spark when coolant is above 95~C and at a high load condition (near W.O.T.). The ECM then checks the signal at "B7" to see if a knock is detected. The functional check is performed once per start-up and if knock is detected when coolant is below 95~C (194~F), the test has passed and the functional check will not be run. If the functional check fails, the "Service Engine Soon" light will remain "ON" until ignition is turned "OFF" or until a knock signal is detected.

This is exactly what is happening.  The light comes on and will stay lit until I shut the engine off. 

I am a little slow on the up-take, but I didn't understand the part about:

The functional check is performed once per start-up and if knock is detected when coolant is below 95~C (194~F), the test has passed and the functional check will not be run.

 

Something in the description that caught my attention is the operating temp; the engine never seems to come up to proper temp (indicates about 150-160 at the dash temp gauge) and the heat doesn't ever actually get past lukewarm.  I am replacing the thermostat this weekend in an attempt to correct and I'm now wondering if low temps might somehow contributing to the SES code problem. 

I need to re-read this a few more times... 

Thanks again for the info VZ!!


Respectfully,

Allen

[RMC_SS_LDO]

Swapped the knock sensor today.  Took it for a quick spin and no codes so far!

Will keep an eye on it, but thanks for the help so far!

/r

Allen

[RMC_SS_LDO]

Awww crap...

Code is back; figuring on replacing the ESC module next.  The lines rang out OK so looking at the next logical step.

Hoping replacing the ESC module and re-setting the timing will also help out the sluggish throttle response.


/r
 
Allen

[joesgarage71]

 The ground in the pic above, Is yours in good shape? Clean

[RMC_SS_LDO]

Rang out pin "D" to chassis ground (alternator housing)... reads a dead short.  Ground looks good... 

[VileZambonie]

Pin D is ground. Whuchu talkin bout willis?

[RMC_SS_LDO]

Pin D is ground. Whuchu talkin bout willis?

Correct.... Based on the images posted above...

I disconnected the connector at the ESC module then took a continuity reading from chassis ground to the 2nd pin in the connector (labled as "D") which read a dead-short.  I guess technically it would be jack "D" since it is within a connector, but that's not how it is labeled in the diagram.

That indicated to me the ground lead going to the ESC is good.

Did I miss something

[VileZambonie]

Did you follow the diagnostic strategy? Do you have access to a scan tool? If all of the circuit checks come out ok replace the ESC module

[RMC_SS_LDO]

I don't have a scan tool, nor do I have access to one.  I have been able to do some basic continuity checks but what I can actually diagnose is pretty basic.  I hate to Easter-egg a problem but I am really out on my own on this.  I ordered the ESC today and will replace tomorrow. 

Other odd problem now; I located and disconnected what I think is the ignition bypass connector (single brown wire by the brake booster) and checked the timing while the engine was warm and is the timing was WAY off.  By way off- it was indicating more than 12 degrees before TDC- the under hood label indicates it should be 0.  I re-set the timing to 0 and now it runs like crap and immediately threw another code 43.    Did I somehow screw up the timing check and adjust or should it actually be set something before TDC as opposed to 0?

I am not sure if the previous owner just backed the timing way off to get it running better because the ESC was toast, but I am wondering now why exactly it's running like crap other than a possibly faulty ESC module.  The distributor, rotor, cables and plugs are all new, but I did not check/set the timing when I swapped them so this was the 1st actual check I've done.

I feel like I've opened Pandora's box here...