U0073 Code on a Cadillac: Control Module Communication Bus A Off (Cadillac Guide)

U0073 on a Cadillac is GM's "Control Module Communication Bus A Off." A module has detected so many errors on its high-speed serial data bus that it has stopped talking on it. That is why U0073 rarely arrives alone: it brings a cluster of "lost communication" codes and symptoms that look unrelated — no crank, gauges dropping out, door locks cycling, a transmission stuck in one gear. GM's Cadillac bulletins trace it to things far cheaper than a module: a backed-out pin in the transmission connector, a loose ground, battery cables, water in a connector and aftermarket accessories. GM's own instruction is not to replace any module until the cause is found.

What Does U0073 Mean on a Cadillac?

Modern Cadillacs run their engine, transmission, brakes, body and dash electronics as separate modules that share information over a serial data network. GM calls its high-speed CAN network high-speed GMLAN. Each module watches its own ability to transmit. When the errors pile up past a limit, the module goes "bus off" — it takes itself off the network rather than keep corrupting it — and stores U0073.

GM's wording has shifted over the years. Its 2019 OBD tables call it "Control Module Communication Bus A Off." The 2015 Escalade bulletin 08-07-30-021H says "Control Module Communications Bus OFF," and the Cadillac PI PIC4740E lists it as "Controller Area Network (CAN) Bus Communication." They are the same code.

In GM's 2019 engine-control tables covering Cadillac engines in the ATS, CTS, CT6, XTS, XT5 and Escalade, the ECM's U0073 entry monitors for a bus A off condition and is listed as Type A — able to turn on the check engine light on the first failure. Another U0073 entry in the same tables is listed as Type B, two trips. Either way, U0073 tells you where the symptom is (the network), not what broke.

Two things follow. First, the module that stored U0073 is usually the victim, not the cause. Second, the other U-codes are clues: which modules went quiet tells a technician which part of the network to look at.

Which Cadillacs Set U0073

GM documents we read name U0073 on these Cadillacs:

• 2007–2014 Escalade models, 2009–2013 Escalade Hybrid and 2007–2009 XLR (08-07-30-021H)
• 2006–2011 STS, 2007–2009 SRX, 2008–2014 CTS (VIN D), 2013–2014 ATS and 2014 CTS sedan (VIN A) with the 6-speed automatic (PIC4740E)
• 2015–2017 Escalade models (PIT5405C) and 2017–2019 Escalade (PIT5586C/F)
• 2014 Cadillac ELR, as a history code that can lead to misdiagnosis (PIC5988)

NHTSA's index also lists a GM PI (PIT-4730A, 2010) with additional diagnostic information for U0140 or U0073 on the 2008–2010 CTS, 2006–2011 DTS, 2006–2011 Escalade models and 2007–2009 SRX. We could read only its summary, so treat that as corroborated.

The Transmission Connector Story

The single most common GM finding for U0073 on a Cadillac is at the transmission, because the high-speed bus runs through the transmission's own connector to reach the TCM.

Escalade and XLR (08-07-30-021H, June 2015). For 2007–2014 Escalades with the 6L80/6L90 six-speed, the 2009–2013 Escalade Hybrid with the 2ML70, and the 2007–2009 XLR, GM lists U0073 with U0100, U0101, U0102, U0109, U0121, U0140 and P0700. The symptoms: MIL and warning lamps, transmission not shifting or defaulting to 2nd gear, intermittent no crank, gauges fluctuating, door locks cycling, chimes sounding, and an engine cooling fan running continuously until the battery goes dead. GM's causes include:

• High-speed GMLAN terminals backed out of the 16-way transmission connector
• The connector's terminal position assurance (TPA) lock not fully seated
• Harness chafed at the transmission case retaining clip
• An open or shorted data link resistor (GM names Data Link Resistor 1 on 2008-and-newer Escalades)
• Corrosion or water intrusion in a control module connector

On the XLR, GM says only the chafed-harness and 16-way connector inspection applies. And GM's "Don't Do This" column is direct: do not replace any control module, wiring harness or component until you have isolated the cause or followed the whole procedure.

STS, SRX, CTS and ATS (PIC4740E, May 2015). On six-speed automatic models GM describes the same family of symptoms — no crank, multiple telltales, reduced power, hard shifts, door locks cycling — and says the TCM or ECM may not communicate with a scan tool at all. The cause is an unseated pin in transmission connector X1. GM's check is to disconnect it and gently tug each wire, warning that side load on the wires can make a loose pin feel locked. U0073 and P0700 are both on GM's code list. See our P0700 Cadillac guide for the transmission side.

Escalade: Grounds, Battery Cables and the Gateway Module

2015–2017 Escalade (PIT5405C, January 2017). GM lists U0073 among more than twenty codes alongside steering that jerks or loses assist, engine stall, a blank instrument cluster, radio or HVAC, door locks cycling and wipers parking in the wrong place. GM notes these are more likely when stopped or turning at low speed, which loads the electrical system. Its causes:

• A poor body control module ground at G218 — check for a loose or cross-threaded nut, or dash insulation trapped under the ground eyelet
• The starter's B+ cable shorting on a loose or misinstalled starter heat shield
• High resistance or loose connections at the battery fuse block or battery cables. GM says the posts should stand 1–2 mm above the clamps, clamp nuts at 7 Nm (62 lb in), and voltage drop on the cables during a steady crank should not exceed 200 mV
• A discharged or faulty battery
• A loose power and ground connection at the electric steering rack (X183 or X133)

That is the clearest GM statement on this page that a battery and cable problem can produce network codes. Our battery replacement guide covers testing and replacement.

2017–2019 Escalade (PIT5586C, June 2019; PIT5586F). Gauges inoperative or fluctuating, no crank, start-then-stall, airbag and suspension messages, a blank radio, dead steering-wheel controls and HVAC — with U0073 among the codes. GM's causes are the Serial Data Gateway Module (SDGM): bent, backed-out or loose terminals at its X1 or X2 connector, and in PIT5586F an SDGM software condition where the module keeps power but stops talking on all its CAN channels. For that, GM's first step on 2017–2018 models is to pull the SDGM power fuse, wait a minute and reinstall it, and it tells dealers not to replace any parts for that condition, pending a software update. GM calls the fuse reset a possibly temporary fix.

Aftermarket Devices, Water and History Codes

Aftermarket modules. NHTSA's index lists a GM bulletin for the 2007 Escalade (07-08-44-004, March 2007) describing aftermarket modules causing LAN communication concerns and codes, no crank, stability messages and PRNDL errors. We could read only the summary, so it is corroborated. It matches what technicians see: remote starters, alarm systems, radio interfaces and devices plugged into the diagnostic port all sit on, or tap into, the network. Unplugging anything aftermarket is one of the cheapest first tests.

Water. GM's 08-07-30-021H lists water intrusion in a control module connector as a cause on 2007 models. Any Cadillac with a leaking windshield, sunroof drain or door seal should have nearby module connectors checked.

History codes. For the 2014 ELR, GM's PIC5988 lists U0073 among history codes that have led to "misdiagnosis or needless component replacement." Its instruction: do not replace or program a component if the codes cannot be duplicated. A U0073 stored in history after a dead battery, a jump start or a module being unplugged during service is not, by itself, a fault.

Is the CUE Radio to Blame?

Usually not for U0073. Cadillac's CUE infotainment problems in the GM bulletin summaries we checked are filed under other codes — radio-inoperative concerns with U0184, and audio-network concerns that GM diagnoses with a separate MOST bus tool. None of them names U0073.

The radio can still be part of the picture: on 2015–2019 Escalades, a blank radio is one of the symptoms GM lists alongside U0073, but the causes GM gives are grounds, battery cables and the gateway module, not the radio. If your CUE screen is cracked or unresponsive to touch, that is a different problem — see our CUE screen delamination guide.

Symptoms of U0073

• Several warning lights and messages at once — StabiliTrak, airbag, suspension, traction
• Gauges dropping to zero, freezing or fluctuating
• Intermittent no crank or no start, or stalling
• Transmission stuck in one gear, defaulting to 2nd, or shifting hard
• Door locks cycling by themselves; chimes sounding
• Radio, HVAC or the instrument cluster going blank
• A scan tool unable to talk to some modules
• A cluster of U-codes such as U0100, U0101, U0121 and U0140 alongside U0073

Causes and How to Confirm Each

How Is U0073 Diagnosed?

1. Scan every module and record which ones set U-codes and which ones do not respond. That map points to the problem area.
2. Note current versus history. GM's ELR guidance: do not replace parts for codes you cannot duplicate.
3. Test the battery and cables first. Low or unstable voltage can knock modules off the bus.
4. Disconnect aftermarket devices, including anything plugged into the diagnostic port.
5. Check the VIN for bulletins that match your model — the list above is a starting point.
6. Inspect the transmission connector on 6-speed and 6L80/6L90 Cadillacs for backed-out pins and the TPA.
7. Check grounds, the data link resistor and bus wiring where GM points; GM's Data Bus Diagnostic Tool helps on later vehicles.
8. Look for water at module connectors near leaks.
9. Replace a module only when it is proven to be the cause, then program it as GM requires.

Parts and Cost

GM Documents That Name U0073 on a Cadillac

Have a dealer check your VIN against current coverages rather than relying on any article, including this one.

What Other U0073 Pages Get Wrong

• "Replace the module that set it." The module that stored U0073 is usually the victim. GM says not to replace modules until the cause is isolated.
• Ignoring the transmission connector. On many Cadillacs the bus runs through it, and GM's fix is a pin.
• Skipping the battery. GM's 2015–2017 Escalade PI lists battery cables, a ground and the battery itself.
• Blaming the CUE screen. CUE concerns in GM's bulletins use other codes.
• Chasing history codes. GM warns against replacing parts for codes that cannot be duplicated.
• Leaving aftermarket gear connected. Disconnect it before paying for diagnosis.

Frequently Asked Questions

Is U0073 serious on a Cadillac?

It can be. GM's Cadillac bulletins link it to no crank, stalling, loss of steering assist on some Escalades and transmissions stuck in a gear. If those symptoms are present, get it diagnosed before relying on the car.

Can a weak battery cause U0073?

Yes. GM's PIT5405C for 2015–2017 Escalades lists a discharged or faulty battery and high-resistance battery cables among the causes of U0073 and related codes. Test the battery and cables first.

Why does my Cadillac show U0073 with P0700?

The transmission's request for the check engine light travels over the same network. GM's PIC4740E and 08-07-30-021H list both codes together and trace them to transmission connector pins.

Can an aftermarket remote start or alarm cause U0073?

It can. A GM bulletin for the 2007 Escalade, which we could see only in summary, describes aftermarket modules causing network communication codes. Disconnect any aftermarket device and recheck.

Should I clear U0073 and see if it comes back?

Record all codes from every module first. Then clearing is reasonable — GM itself warns against replacing parts for history codes that cannot be duplicated. If it returns, the module map tells you where to look.

Does U0073 mean my CUE radio is failing?

Not usually. In GM's bulletins we checked, CUE and radio concerns are diagnosed under other codes such as U0184. A blank radio can be one symptom of a network fault, but GM's listed causes are elsewhere.