legacycentral bbs

What might explain the low voltage on the pressure sensor connector?

Broken or degraded wiring somewhere in your harness.

I'd run a new 12v to that wire and see if it works.

I think you may be getting things mixed up. The pressure sensor (aka MAP sensor) should have three wires going to it, 5v reference voltage, sensor ground, and signal voltage. There should NOT be 12v to the pressure sensor.

The pressure exchange solenoid on the other hand should have 12v to it, while the other wire for the pressure exchange solenoid goes to the ECU. The ECU grounds the pressure exchange solenoid, which completes the circuit and opens the solenoid.

I would agree, it sounds like you have bad wiring somewhere in the pressure exchange solenoid wiring.

finally was able to dig into things today. Measured the voltage between ecu connector and body - 11.7V. Measured the voltage between ECU terminal and body, 5.4V. Unless I have overlooked something this tells me there is an issue with the ECU and not the wiring.

Which connector & pins are you testing? Are you following a procedure in the FSM?

Please list what specific pins & connectors you're testing.

pin/terminal 20 in connector F47 at the ecu for the pressure solenoid.

Bryan,

The manual states that there should either be 0 V or 10 - 13 V on Connector F47, pin No. 20. This is because the ECU switches voltages on and off depending on engine running conditions.

You need to check the resistance of the wiring itself. Remove the F47 connector and check the resistance of the wire from pin 20 to connector B130, pin 1 (pressure exchange solenoid connector, pin 1 is the green wire with yellow stripe). The restance should be 0 ohms or very close to it.

Have you checked for 12v on the B130, pin 2 connector when the ignition key is in the "ON" position? If not, check that.

It was a steady 4-5V on terminal 20 on the ECU, measured it several times just to make sure. Resistance on the communication wire was 0.02 ohms and I will check voltage on the B130 connector, pin 2 later this morning and report back.

Just measured voltage on connector B130, pin 2 at a solid 11.95V.

I think now all fingers now point at the ECU.

Unless you're monitoring the voltage on terminal 20 while driving over several minutes, I still wouldn't jump to the ECU quite yet.

The other thing to note is that the ECU triggers that solenoid by grounding that ECU pin so there is a voltage differential across the pressure exchange solenoid so it can operate. This logic is backwards from what most non-electrical people think happens. The ECU doesn't supply power to the device, rather it "sinks" power or provides a ground. Transistors handle this arrangement much better.

So what would be my next step?

I would suggest monitoring the voltage of that ECU pin while driving around. Run a small skinny wire into the back side of that ECU pin and then hook up your multi meter to read voltage. Drive around for a little bit and see if the voltage reading changes at all. It'd be good to have a friend or someone watch the multi meter while you drive.

If the voltage changes does that mean bad ecu?

No, it means it's working fine.

Have you tried connecting the green diagnostic connectors to see if the pressure exchange solenoid clicks/operates? Sorry, I don't recall if you said you already did this.

If it appears to be working, then I would check the MAP sensor since it displays the same code.

with the green diag connectors would the solenoid still click even though its not getting power from the B130 connector?

You posted above that there was power at the B130 connector?

2.2TLegacy wrote:Just measured voltage on connector B130, pin 2 at a solid 11.95V.

The solenoid should click if you measured power on pin 2 of the B130 connector.

Replaced the solenoid today, didn't solve the issue. So now its down to the MAP sensor or the ECU itself.

Fixed it.

Remember car repair 101? Always check and double check the easy things first. The vacuum line going from the pressure sensor to the solenoid had a small, small crack in it, so when I did a visual inspection of it, i didn't notice it. Went out on a limb, swapped out the line and viola, problem fixed.

I laughed so hard when after all this diagnostic work I have done and its a 5" piece of vacuum line that was the problem all along.

On the plus side, I do know a hell of a lot more about electrical work on this car than before.

Nice! That would definitely cause it! Good find.

Yup....always start with the easy stuff first

annnnnnd the problem is back...time to replace all vacuum and boost lines. I'll report back if that solves it, otherwise I am going to be on the hunt for a pressure sensor.

replaced every vacuum and boost line, issue is still there. New symptom though, when I start the car, it starts fine, check engine light is off and then a few seconds later there is a single "click" sound that comes from the engine bay, the rpms drop and the check engine light comes on.

Pretty vague, I know but any thoughts?

What code is stored when the CEL comes on?

Same one...45

Did you check the resistance of the wiring for the MAP sensor?