DTC P1545 A/C relay diagnosis

Tiny
TITANG9
  • MEMBER
  • 2005 GMC CANYON
  • 3.5L
  • 5 CYL
  • 2WD
  • AUTOMATIC
  • 48,000 MILES
P1545 code. The compressor runs fine when jumped directly at relay 50. The A/C request at BCM only works when the evaporator temp sensor is jumped directly (Autel Maxisys Elite scanner). Swapped relays, no joy. Cleaned both fender grounds, still nothing. How to test harness from PCM to relay and or to BCM?
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Tuesday, January 14th, 2020 AT 5:08 PM

6 Replies

Tiny
ASEMASTER6371
  • EXPERT
Good morning,

I attached a diagram for you. If you bypassed the evap temperature sensor, that sounds like your issue. I may be open. The sensor sends a signal to the BCM and the BCM sends a signal to the ECM to ground the control side of the relay.

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Roy

REMOVAL PROCEDURE
1. Remove the radio.
2. Remove the mounting screw from the evaporator temperature control module.
3. Disconnect the electrical connector from the control module.
4. Cut the evaporator temperature sensor wire near the control module.

IMPORTANT: If you are replacing only the control module, proceed to Step 4 of the Installation Procedure.

5. Remove the evaporator core.

imageOpen In New TabZoom/Print

6. Using needle nose pliers, carefully remove the evaporator temperature sensor from the evaporator core.
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Wednesday, January 15th, 2020 AT 3:57 AM
Tiny
TITANG9
  • MEMBER
Thanks, however, even when sensor was jumped the A/C still did not work. One more thing, when trying to activate the #50 A/C relay with the Autel Scanner, the message is: "Engine Speed Too High". By the way, the engine is off.
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Wednesday, January 15th, 2020 AT 6:39 AM
Tiny
ASEMASTER6371
  • EXPERT
The ground for the control side of the relay is controlled by the ECM. It will ground the relay and activate the compressor once the inputs from the sensors are credible.

Did you verify the pressures for the AC system? Can you give me the pressures when the engine is off and when it is running?

https://www.2carpros.com/articles/car-air-conditioner-not-working-or-is-weak

Roy
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Wednesday, January 15th, 2020 AT 6:49 AM
Tiny
ASEMASTER6371
  • EXPERT
Here is the information on the 1545.

Roy

DTC P1545

CIRCUIT DESCRIPTION
Ignition voltage is supplied directly to the A/C compressor clutch relay. The powertrain control module (PCM) controls the relay by grounding the control circuit through an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line which is monitored by the PCM. When the PCM is commanding a component ON, the voltage of the control circuit should be near 0 volts. When the PCM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be near battery voltage.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC P1545 Air Conditioning (A/C) Clutch Relay Control Circuit.

CONDITIONS FOR RUNNING THE DTC
The ignition voltage is between 9-18 volts.
The PCM driver is activated for at least 0.5 second.

CONDITIONS FOR SETTING THE DTC
The PCM detects an improper voltage level on the output circuit that controls the A/C relay.

ACTION TAKEN WHEN THE DTC SETS
The PCM will not illuminate the malfunction indicator lamp (MIL).
The PCM stores the failure records.
The A/C compressor clutch is disabled.

CONDITIONS FOR CLEARING THE DTC
The diagnostic trouble code (DTC) will become history if the PCM no longer detects a failure.
The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
The DTC can be cleared with a scan tool.

TEST DESCRIPTION

Steps 1 - 13
imageOpen In New TabZoom/Print

Step 14
imageOpen In New TabZoom/Print

The numbers below refer to the step numbers on the diagnostic table.
3. Listen for an audible click when the A/C compressor clutch relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
4. This step tests for voltage at the coil side of the A/C compressor clutch relay. A 15-amp fuse supplies power to the coil side of the A/C compressor clutch relay.
5. This step verifies that the PCM is providing ground to the A/C compressor clutch relay.
6. This step tests if ground is constantly being applied to the A/C compressor clutch relay.
13. Perform the programming procedure for the PCM.
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Wednesday, January 15th, 2020 AT 6:54 AM
Tiny
TITANG9
  • MEMBER
Thanks Master, last question: I should have continuity between the C7-F5 pin (D-GN/WH) at Relay 50, and the #6 pin (D-GN/WH) at PCM?
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Friday, January 17th, 2020 AT 12:24 PM
Tiny
ASEMASTER6371
  • EXPERT
Correct. Make sure there is power to the other side of the control side of the rely.

That is the ground side of the relay. The PCM grounds that pin.

Roy
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Friday, January 17th, 2020 AT 12:31 PM

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